Hardware - IDE-BUS: description of the IDE bus and HDD commands.

IDE-BUS.            
                               
music by MIDISOFT              
Information provided by V. Eliseev.        
________________________________
                               
   Dfor those who want more details
to get acquainted with the work of the hard drive, we bring
Here's a description of the IDE bus and HDD commands.      
                               
+--------+----------+--------+-----------------------------+
| Contact| Direction | Signal | Function |
+--------+----------+--------+------------------------------+
|  1 | Out | Reset | - Host reset  |
|  3 |I/O | HD7 | Host data bus 7  |
|  5 |I/O | HDb | Host data bus b  |
|  7 | I/O | HDS    | Host data bus 5               |
|  9     |   I/O    | HDЧ    | Host data bus 4               |
| 11     |   I/O    | HDЗ    | Host data bus 3               |
| 13     |   I/O    | HD2    | Host data bus 2               |
| 15     |   I/O    | HD1    | Host data bus 1               |
| 17     |   I/O    | HDO    | Host data bus 0               |
| 19     |    -     | Ground |                               |
| 21     |   In     | DMARQ  | DMA Request                   |
| 23     |   Out    | -IOW   |- Host I/O Write              |
| 25     |   Out    | -IOR   | - Host I/O Read               |
| 27     |   In     | IOCHRDY|                               |
| 29     |   Out    | DMACK  | - DMA Acnowelege              |
| 31     |   In     | IRQ    | - Host interrupt request      |
| 33     |   Out    | HA1    | Host adress bus 1             |
| 35     |   Out    | HAO    | Host adress bus 0             |
| 37     |   Out    | -CSO   | - Host chip select 0          |
| 39     |   I/O    | -ACTIV | - Drive active                |
+--------+----------+--------+-------------------------------+
|  2     |    -     | Ground |                               |
|  4     |   I/O    | HD8    | Host data bus 8               |
|  б     |   I/O    | HD9    | Host data bus 9               |
|  8     |   I/O    | HD10   | Host data bus 10              |
| 10     |   I/O    | HD11   | Host data bus 11              |
| 12     |   I/O    | HD12   | Host data bus 12              |
| 14     |   I/O    | HD13   | Host data bus 13              |
| 1б     |   I/O    | HD14   | Host data bus 14              |
| 18     |   I/O    | HD15   | Host data bus 15              |
| 20     |    -     | Key    |                               |
| 22     |    -     | Ground |                               |
| 24     |    -     | Ground |                               |
| 2б     |    -     | Ground |                               |
| 28     |   Out    | ALE    |                               |
| 30     |    -     | Ground |                               |
| 32     |   In     | -HIO1б | - Host 1б-bit I/O chip select |
| 34     |   I/O    | -PDIAG |                               |
| 3б     |   Out    | HA2    | - Host adress bus 2           |
| 38     |   Out    | -CS1 | - Host chip select 1  |
| 40 | - | Ground |                               |
+--------+----------+--------+------------------------------+
                               
 1.  Signals whose source is
main machine (HOST), are weekends
mi, and the source of which is NMD -
input.                                
 2.  Signals active at low level
are marked with the prefix "-".                 
                               
 Below is a description of the signals        
 IDE interface.                        
                               
 -RESET  - reset signal from the main machine
us.                                      
                               
 Host data bus 0-15 - 16 bit two-
directional data bus. Low 8 bits,
HDO-HD7, used to access re-
histram.  All 16 bits are used to transfer
data transfer.                           
Ground  -  Ground connections between NMD and
main machine.                         
 KEY - Key. Used for privilege
cable orientation                        
 -IOW - Recording strobe, trailing edge
which data on HDO-HD15 lines is fixed
are registered in NMD registers.                  
 -IOR - Reading strobe, low level co-
which allows the transfer of data from the re-
ructpob NMD to the host machine data bus
us. Falling edge -IOR captures data from
NMD to the main machine.                   
 IRQ - Host machine interrupt signal.
Interruption is possible when the device is selected
swarm, and the main machine installs
-IEN bit in the Fixed Disk Register (address
3F6).  When no device is selected or
-IEN is not active, this output is in
high impedance state. IRQ set
is supplied by the drive microcontroller.
IRQ is reset to zero during operations
reading the host machine from the status register
tion or during a write operation in Command Re-
gister. Line with threestates.       
DAO,DA1,DA2 - Address lines used
to select a register in the task file.      
 -CSO - Crystal selection 0, decoding signal
controlled from the bus of the main machine. Using
Used to select registers with lower ad-
pecamu in the task file.                   
 -CS1 - Crystal selection 1, decoding signal
controlled from the bus of the main machine. Using
Used to select registers with higher ad-
pecamu in the task file.                   
 -HIO16  -  Signal from the NMD, informing
main machine, which is a 16-bit register
data is selected and that the NMD is ready to accept or
transmit a 16-bit data word. Line with
three states.                       
 -ACTIVE - Line from NMD, used for
turning on the LED when the main machine
does not access the disk.          
 DMARQ - Direct memory access request.
 -DMACK  - Request confirmation signal
RAP.                                     
                               
Note.                              
                               
 1. DMARQ and DMACK signals are reserved
for future use.             
                               
Required signal timing relationships 
           in the IDE interface:            
                               





















                               
Note. All tenses are given in HC.       
                               
     Address decoding.     
                               
 The main machine is addressed to the NMD, using
using programmable I/O. When
this register address has three address lines
DAO-DA2 and choice of crystal -CSO or
-CS1. Main machine data bus HD8-HD15
only allowed when signal is active
-HIO16 and the host machine addresses the register
data for data transfer.              
   A set of registers accessible from the outside
main machine, called task file
(Task File).                             
   Table 4.3 shows the addresses and functions
tions of registers.                           
                               
                             Table 4.3
+----+----+---+---+---+----+----+
|-CSO|-CS1|DA2|DA1|DAO|  Read function | Recording function ||----+----+---+---+---+------------------+-------------------+
| 1  | 0  | 0 | X | X | высокий импеданс | не используется   |
| 1  | 0  | 1 | 0 | X | высокий импеданс | не используется   |
| 0  | 1  | 0 | 0 | 0 | Data Register    | Data Register     |
| 0  | 1  | 0 | 0 | 1 | Еггог Register   | не используется   |
| 0  | 1  | 0 | 1 | 0 | Sector Count     | Sector Count      |
| 0  | 1  | 0 | 1 | 1 | Sector Number    | Sector Number     |
| 0  | 1  | 1 | 0 | 0 | Cylinder Low     | Cylinder Low      || 0  | 1  | 1 | 0 | 1 | Cylinder High    | Cylinder High     |
| 0  | 1  | 1 | 1 | 0 | SDH Register     | SDH Register      |
| 0  | 1  | 1 | 1 | 1 | Status Register  | Command Register  |
| 1  | 0  | 1 | 1 | 0 | Alternativ status|Fixed Disk Registr |
|    |    |   |   |   | Register         |                   |
| 1  | 0  | 1 | 1 | 1 | Digital Input    | не используется   |
|    |    |   |   |   | Register         |                   |
+----+----+---+---+---+------------------+-------------------+
                               
 Примечание. X - состояние безразлично.  
                               
      Описание регистров.      
                               
   Ниже дано описание регистров интерфей-
са IDE.Unused bits in read registers
are perceived as zeros, in write registers
the state of these bits is indifferent. If
bit is active, it is set to "1",
if inactive, then set to "0".                
                               
   Data Register.              
                               
   Data register. Through this register
data is hidden and written in commands
reading and writing. Through this register, recording
The sector rotation table is created in
formatting command and data associated
with the identification command. All data
transmitted in 16-bit words, except
error correction code (ECC) bytes.
The data is stored on disk in the following sequence:
leads: low byte first,
then the high byte.                      
                               
   Eggrog Register.             
                               
   The error register contains the status of the
the last command executed by the NMD. Contents
This register is only valid
when the Status Register is set to
bit 0 - ERR.                             
   After executing the diagnostic command
(code 90) register contains the status code. 
                               
   The following describes the bits in the Error Register. 7 6 5 4 3 2 1 0       
+---+---+---+----+---+----+----+----+    
|BBK|UNC| - |IDNF| - |ABRT|TRKO|DMNF|    
+---+---+---+----+---+----+----+----+    
                               
 BBK - Bad Block Mark                  
 - indicates that a bad mark has been found
block in the required identifier field
sectors.                                 
UNC - Uncorrectable Data Error        
 - indicates that hekoppektu is taking place-
Possible data error.                    
 IDNF - ID Field Not Found              
 - indicates that the field was not detected
ID of the required sector.       
ABRT - Abort                           
 - indicates that the required commandwas
interrupted due to invalid co-
yes commands, or unreadiness or errors
NMD records.                              
 TRKO - Track 0 Not Found               
 - indicates that track 0 is not detected
during a recalibration command.           
 DMNF - Data Adress Mark Not Found      
 - indicates that the data address marker
not found after ID required
my sector.                            
                               
   Sector Count.               
                               
   The sector counter determines the number
data sectors for read/write command
si.  If the value in this register is
0, then the value of 256 sectors is determined.
This counter decreases as you read
recording/recording of each sector.  Contents
this register determines the number of sectors
on the track when executing the Initia- command
lize Drive Parameters.                    
                               
   Sector Number.              
                               
   Sector number.  This register contains
numberinitial sector for any pre-
stupid to NMD. When processing is completed, sec-
torus and at the end of the command this register indicates
calls for last correctly read
sector or to the sector in which it occurred
error.                                  
                               
   Cylinder Low                
                               
   Register of the lower digits of the ci number
lindra contains the lower 8 digits on-
initial cylinder number for any
attitude towards NMD.  When processing is complete
sectors and at the end of the command this register
changes and displays the current qi number
lindra.                                  
                               
 Cylinder High               
                               
   Register of the most significant digits of the ci number
lindra contains 3 senior digits
cylinder number for any operation
to NMD. When processing of the sector is completed and
at the end of the command this register is changed and
displays the current cylinder number.       
                               
   SDH Register                
                               
 7 6 5 4 3 2 1 0          
+---+---+---+---+---+---+---+---+        
| 1 | 0 | 1 |DRV|HSЗ|HS2|HS1|HSO|        
+---+---+---+---+---+---+---+---+        
                               
 DRV - Drive Select Number - 0          
 - selected NMD 0, 1 - selected NMD 1        
HSЗ-HSO                                
 - binary coded selection number
heads.                                 
                               
 Status Register             
                               
   This register contains information o
condition of NMD. Contents of the change register
Fires at the end of each command. EU-
If the BSY bit is active, then the other bits are not
are valid. Read by host machine
this register confirms its receipt
interrupts and resets the received interrupt
tearing                                 
                               
 7 6 5 4 3 2 1 0   
+----+----+----+----+----+----+----+----+
|BSY |DRDY|DWF |DSC |DRQ|CORR|IDX |ERR |
+----+----+----+----+----+----+----+----+
                               
 BSY - Busy                              
 - If this "busy" bit is active, then the mic
The storage controller has access to
registers of the task file, and the main machine
no. Any reading by the main machine of the register
reading the task file results in reading Status
Register.                                
 DRDY - Drive Ready                      
 - Drive readiness indicator.       
 DWF - Drive Write Fault                
 - This bit indicates that the drive has
a recording error occurred.                 
DSC - Drive Seck Complete              
 - This bit indicates that the heads are installed
updated on the required track.            
DRQ - Data Request                      
 - Data request.  Indicates thatNMD is ready to transmit a word or data byte
data on the data bus.                      
 CORR - Corrected Data                  
 - NMD sets this bit to "1" if
a data error occurred and this error was
adjusted.                         
IDX - Index                            
 - Index.  This bit is active once per
disk revolution.                            
ERR - Error                            
 - Error bit. Indicates to the main machine
what happened during the last operation
error. The bits in the Error Register provide
for additional information.            
                               
   Command Register.           
                               
   Command register. Home to this register
the machine writes an 8-bit command code
dy, which will be performed by the NMD.         
   Command execution starts immediately
after the registration has been made to the register
writing                                    
                            Таблица 4.4
+-----------------------------------+---+--------------------+
|                                   | К |    Регистры        |
|         Команда                   | о +----+----+----+-----+
|                                   | д | SC | SN | CN | SDH |
|-----------------------------------+---+----+----+----+-----+
|Recalibrate                        | 1X|    |    |    | DRV |
|Read Sector(s) (с повторами)       | 20| V  | V  | V  |  V  |
|Read Sector(s) (без повторов)      | 21| V  | V  | V  |  V  |
|Read Long (с повторами)            | 22| V  | V  | V  |  V  |
|Read Long (без повторов)           | 23| V  | V  | V  |  V  |
|Read Verify Sector(s)(с повторами) | 40| V  | V  | V  |  V  |
|Read Verify Sector(s)(без повторов)| 41| V  | V  | V  |  V  |
|Write Sector(s) (с повторами)      | 30| V  | V  | V  |  V  |
|Write Sector(s) (без повторов)     | 31| V  | V  | V  |  V  |
|Write Long (с повторами)           | 32| V  | V  | V  |  V  |
|Write Long (без повторов)          | 33| V  | V  | V  |  V  |
|Format Track                       | 50| V  |    | V  |  V  |
|Seek                               | 7X|    | V  | V  |  V  |
|Execute Drive Diagnostic           | 90|    |    |    | DRV |
|Initialize Drive Parameters        | 91| V  |    |    |  V  |
|Read Sector Buffer                 | E4|    |    |    | DRV |
|Write Sector Buffer                | E8|    |    |    | DRV |
|Identify Drive                     | EC|    |    |    | DRV |
+-----------------------------------+---+----+----+----+-----+
                               
Примечание.                              
                               
 1. X - означает, что значение битов без-
различно;                                
    V  - означает, что данный регистр ис-
пользуется.                              
   Регистры: SC - Sector Count          
             SN - Sector Number          
            CN - Cylinder Low & High   
            SDH - SDH Register          
                               
   DRV -  means that in the SDH Register
Only the DRV bit is used, all others
bits are not valid.                   
 2. Commands are given in hexadecimal system
topic.                                    
 3.  "With repetitions" means that in the command
x Writes and Reads identifier search
carried out for 10 index pulses
owls, and “no repetitions” - for 2.         
                               
   Alternativ Status Register. 
                               
   Alternate status register
crashes with Status Register, but is configured to
other addresses.  The only difference from
Status Register iswhat reading this
register does not lead to confirmation of pre-
tearing or clearing the interrupt request.  
                               
 7 6 5 4 3 2 1 0   
+----+----+----+----+----+----+----+----+
|BSY |DRDY|DWF |DSC |DRQ |CORR|IDX |ERR |
+----+----+----+----+----+----+----+----+
                               
A description of the bits of this register is given in the description
sania Status Register.                   
                               
   Fixed Disk Register.        
                               
   This register is used for programming
frame reset of NMD and for control of dis-
interrupt solution.                     
                               
 7 6 5 4 3 2 1 0  
+----+----+---+---+-------+----+----+---+
| 0 | 0 | 0 | 0 |HSЗEN=1|SRST|-IEN| 0 |
+----+----+---+---+-------+----+----+---+
                               
 HSЗEN - Head Select 3 Enable           
 - “1” is always written to this bit.   
 SRST - Host Software Reset              
 - soft reset - working out this
bit leads to NMD reset.              
 -IEN - Interrupt Enable                
 - interrupt enable. When -IEN=0 and
NMD is selected, then the production of pre-
jerking on the IRQ output. When -IEN=1, then
IRQ output to high impedance state.    
                               
   Digital Input Register.     
                               
   This register shows which NMD
selected and which head is currently selected
moment.                                  
                               
 7 6 5 4 3 2 1 0  
+----+----+----+----+----+----+----+----+
|HIZ |-WTG|-HSЗ|-HS2|-HS1|-HSO|-DS1|-DSO|
+----+----+----+----+----+----+----+----+
                               
 HIZ                                    
 - when this register is read, the output is DD7
is set to a state of high im-
pedance. -WTG - Write Gate                      
 - NMD produces -WTG during commands
records.                                  
 (-HSЗ)-(-HSO) - Head Select            
 - Binary's complement to the selected address
heads.  For example, if HSЗ-HSO=1010, then
5th head selected.                     
 -DS1,-DSO - Drive Select               
 - Shows which of the two drives
selected and active at this time.         
                               
       Description of commands.        
                               
   All commands are decoded from Command
Register.                                
   To give a command, you must register
load the corresponding registers in the file
tasks, activate the enable bit
tear -IEN and write the command code in
Command Register. Execution of command on-
starts after writing the command in Command
Register.                                
                               
   Recalibrate.                
                               
   This command moves the recording heads
si/read to cylinder 0. Having received the command,
NMD installs BSY and searches
cylinder 0. Then the NMD waits for the end
search, updates register state
task file, clears BSY and generates
interruption                              
   Table 4.7 shows the communication protocol
for this command.                      
                               
   Read Sector(s)              
                               
   These commands allow you to read from 1
up to 256 sectors of 512 bytes, starting from
sector specified in Sector Number. If
Sector Count = 0, then it will be read
256 sectors.                            
   Table 4.5 shows the exchange protocol
for these commands.                       
   If the NMD is not on the selected
horn, a search is carried out. If NMD is on-
walks on the selected track, then
is the search for an identifier for 2 in-
dex pulses, for Read Sector(s) without
repetitions and for 10, for Read Sector(s) with
repetitions.  If the ID is read correctly, then
the data field synchronization byte must
be found before the next impulse of the secto-
ra, otherwise a DMNF error will be issued.
Until the command completes, the file registers are
dachas contain roomcylinder, head and
sectors for last read sec-
tora.  If an error occurs, then read
stops at the sector where this error occurs
discovered.  In this case, the file registers
tasks contain the number of the cylinder, head and
sector where the error occurred. Sector Co-
unt contains the number of untransferred sectors.
If this error was a hekoppek error-
data, then this data will be accessible
are difficult for the main machine to read, and
Talent sectors will not be transferred.   
   After the command completes successfully
Sector Count = 0.                        
   If the Read Long command is executed, then
NMD does not check ECC bytes to determine
error in the data field. NMD returns
to the main machine not only data, but also 7
error correction byte (ECC). Data Bytes
are transmitted in 16-bit parcels, and the bytes
ECC - 8-bit.                         
   Read Long commands are always single-sector
teams.                                 
                               
    PROTOCOL FOR EXECUTING READ COMMANDS   
                               
                             Table 4.5
+---+-----------+-----------------------------+
|STEP|   MAIN MACHINE |         NMD ||---+--------------------------+-----------------------------+
|1  | Проверка, что BSY=0 и    |                             |
|   | DRDY=1                   |                             |
|2  | Запись в регистры:       |                             |
|   |  Sector Count            |                             |
|   |  Sector Number           |                             |
|   |  Cylinder Low            |                             |
|   |  Cylinder High           |                             |
|   |  SDH                     | |
|3 | Record in CommandRegister |  |
|4 |   |Sets BSY=1  |
|5 |   |Preparing for data transfer |
|   |   |(loads data into the buffer  |
|   |   |data)  |
|b |   |Sets DRQ=1,BSY=0 and  |
|   |   |generate IRQ  |
|7 | Reads Status Register  | |
|8 |   |Resets IRQ  |
|9 | Reads a data block  |  |
|10 |   |Sets DRQ=0  |
|11 |   |If a multi-sector command, |
|   |   |then return to step 4  |
|12 | Ready for the next one  |  |
|   | command  |  |
+---+-----------+----------------------------+
                               
Note.  This protocol is applicable to
the following commands:                      
                               
       Identify Drive                   
       Read Buffer                      
       Read Sector(s).                   
                               
   Write Sector(s)             
                               
   These commands allow you to write from 1
up to 256 sectors of 512 bytes, starting from
sector specified in Sector Number. If
Sector Count = 0, then 256 will be written
sectors.                                
   Table 4.6 shows the communication protocol
for these commands.                         
   If the NMD is not on the selected
horn, a search is carried out. If NMD is on-
walks on the selected track, then
is the search for an identifier for 2 in-
dex pulses, for Write Sector(s)
no repetitions and for 10, for Write Sec-
tor(s) with repetitions. If the ID is not found, then
IDNF error is set.             
                               
    PROTOCOL FOR EXECUTING RECORDING COMMANDS   Таблица 4.6
+---+--------------------------+-----------------------------+
|ШАГ|   ГЛАВНАЯ МАШИНА         |         НМД                 |
|---+--------------------------+-----------------------------+
|1  | Проверка, что BSY=0 и    |                             |
|   | DRDY=1                   |                             |
|2  | Запись в регистры:       |                             |
|   |   Sector Count           |                             |
|   |   Sector Number          |                             |
|   |   Cylinder Low           |                             |
|   |   Cylinder High          |                             |
|   |   SDH                    |                             |
|3  | Запись в CommandRegister |                             |
|4  |                          |Устанавливает DRQ=1          |
|5  | Читает Status Register   |                             |
|   | (DRQ=1)(необезательно)   |                             |
|б  | Записывает блок данных   |                             |
|   | в Data Register          |                             |
|7  |                          |Sets DRQ=0,BSY=1  |
|8 |   |Processing data  |
|9 |   |Sets BSY=0, select-  |
|   |   |sets IRQ and sets  |
|   |   |DRQ=1, if transmitted  |
|   |   |one more data block  |
|10 | Reads Status Register  |  |
|   | (in response to IRQ)  |  |
|11 |   |Resets IRQ  |
|12 |   |If a multi-sector command, |
|   |   |then return to step 5  |
|13 | Ready for the next one  |  |
|   | command  |  |
+---+-----------+----------------------------+
                               
Note:  This protocol is applicable to
the following commands:                      
                               
 Format Track                      
       Write Buffer                      
       Write Sector(s).                  
                               
   If the ID is read correctly, the data is recorded
armed inbuffer, written to field
sector data accompanied by internal
generating ECC code. If it happened
error while writing more than one
sector, then recording stops at sector
re where the error occurred and the task file
contains the number of the cylinder, head and section
where the error occurred. Upon completion
command registers contain cylinder numbers
ra, heads and sectors corresponding
the last recorded sector.          
   After the command completes successfully
Sector Count = 0.                        
   It is necessary to take into account that NMD may
remove additional blocks from the machine
data to ensure high performance
body recording. The Write Long command writes
sends data and 7 bytes ECC directly from the buffer
ra sector, while the NMD itself does not generate
no ECC bytes. Data bytes are transmitted over
16-bit links, 8-bit ECC bytes. Teams
Write Long is always single-sector commands. 
                               
   Read Verify Sector(s).      
                               
   This command is identical to Read Sector(s),
except that the data is not transferred
are given to the main machine.                 
                               
      COMMAND EXECUTION PROTOCOL,      
     HE USING TRANSMISSIONДАННЫХ     
                               
                              Таблица 4.7
+---+--------------------------+-----------------------------+
|ШАГ|   ГЛАВНАЯ МАШИНА         |         НМД                 |
|---+--------------------------+-----------------------------+
|1  | Проверка, что BSY=0 и    |                             |
|   | DRDY=1                   |                             |
|2  | Запись в регистры:       |                             |
|   |   Sector Count           |                             |
|   |   Sector Number          |                             |
|   |   Cylinder Low           |                             |
|   |   Cylinder High          |                             |
|   |   SDH                    |                             |
|3  | Запись в CommandRegister |                             |
|4  |                          |Устанавливает BSY=1          |
|5  |                          |Выполняет действия соответ-  |
|   |                          |ствующие команде             |
|б  |                          |Устанавливает BSY=0 и        |
|   |                          |вырабатывает IRQ             |
|7  | Reads Status Register  |  |
|8 |   |Resets IRQ  |
|9 | Ready for the next one  |  |
|   | command  |  |
+---+-----------+----------------------------+
                               
Note:  This protocol is applicable to
the following commands:                      
                               
       Execute Drive Diagnostic          
       Read Verify Sector(s)            
 Recalibrate                      
       Seek                              
       Initialize Drive Parameters.      
                               
   Format Track.               
                               
   This command formats the track by
given in the task file. Track address op-
determined by the value in Cylindr High & Cy-
linder Low Registers, and the number of sects
ditch is defined in Sector Count. When you-
the command is being processed, NMD installs
DRQ bit and waits for input from the master
machine 512 byte data format. When
data received, NMD awaits DRQ, set
enters BSY, starts executing commands
yes. If the NMD is not at a given level,
horn, starts searching for a track.
When the NMD is on a given track,
NMD starts formatting using
data received from the host machine.    
   Contents of data received from the heads-
noy machine, are interpreted as follows
way:                                 
                              Table 4.8
 +-----------------+------------------+
 |DD15-DDO8  |     DDO7-DDO |
 +-----------------+------------------+
   |            первый сектор           |
   +-----------------+------------------+
   |номер сектора    |      дескриптор  |
   +-----------------+------------------+
   |        последний сектор            |
   +-----------------+------------------+
   |номер сектора    |      дескриптор  |
   +-----------------+------------------+
   |оставшиеся байты записываются нулями|
   +------------------------------------+
                               
   Each sector is characterized by 16-bit
in a word. DD15-DD8 contain the sec number
tora.  Typically the sector numbers follow
order, starting from 1, to ensure
sector editing 1:1. DD7-DDO contain
descriptor number, where:                   
   00H - sector formatting as good
shego;                                    
   80H - formatting the sector as a flat
xoro.                                    
   Values other than 00 and 80 uhtepnpe-
rated as good sectors.            
   Table 4.6 shows the protocol for
this command.                          
                               
   Seek.                       
                               
   This command initiates a search for
horns and selects the head defined in
task file. To run this command
NMD does not have to be formatted
van.                                     
   NMD can generate interrupts up to
complete the search.                       
   Table 4.7 shows the protocol for
this command.                          
                               
 Execute Drive Diagnostic.   
                               
   Perform diagnostics of NMD. After half-
The execution of this command is carried out internally by the NMD.
tion tests. After performing diagnostics in
Error Register 8-bit code described
below:                                    
                               
   code  description                    
                               
   01  no errors                  
   02  controller error          
   03  sector buffer error       
   05  microcontroller error      
                               
   Note: NMD can issue in chief
car and other codes, the meanings of which
ry are specified at the design stage.  
   Table 4.7 shows the protocol for
this command.Initialize Drive Parameters.
                               
   Initialization of NMD parameters. Allow-
The control machine cannot set the number
sectors per track and the maximum number
heads that should be emulated
NMD.  Upon receiving the command, the NMD will install
BSY, saves these parameters, clears
BSY and generate an interrupt.            
   This command only uses re-
hysteres Sector Count, which indicates
maximum number of heads. DRV bit is off
sets accordingly NMD 0 or NMD 1. Sec-
tor Count and SDH Register are not checked
for the correctness of this command. If they
are not correct, there will be no error message
be issued before any task is completed
manda using these values.        
   Table 4.7 shows the protocol for
this command.                          
                               
   Read Buffer.                
                               
 Reading a buffer. Allows the main machine
do not read 512 bytes of data from the sec buffer
torus NMD. Upon receipt of this command, NMD
sets BSY, prepares buffer
for a read operation, sets DRQ,
waits for BSY, generates an interrupt. Head-
The machine then reads the data bytes
from this buffer.Table 4.6 shows the protocol for
this command.                          
                               
   Write Buffer.               
                               
   Write buffer. This command allows
host machine overwrite contents
NMD data buffer.                       
   Table 4.6 shows the protocol for
this command.                          
                               
   Identify Drive.             
                               
   Identify NMD. Allows head-
receive information o from the NMD
German Upon receipt of this command, the NMD installs
sets BSY, writes to the data buffer
formation, sets DRQ and generates
interruption  The main machine reads this
information from the buffer.                    
                               
   Structure of returned NMD information
looks like this.              
                               
Byte Contents                                   
                               
00-01 HEX ?                                             
02-03   HEX     количество цилиндров                          
04-0б   HEX     0                                             
07      HEX     количество головок                            
08-09   HEX     байт на дорожке                               
OA-OB   HEX     байт на сектор                                
0C      HEX     0                                             
0D      HEX     секторов на дорожке                           
0E-13   HEX     ? 14-27   ASCII   Serial Number (конец со-                      
                общения 00h)                                  
28      HEX     0                                             
29-2D   HEX     ?                                             
2E-35   ASCII   Firmware Revision                             
Зб-SD   ASCII   Model Number (конец со-                       
                общения 80h)                                  
                               
   В ячейках, где числа занимают два бай-
та,  информация  располагается  следующим
образом: в младшей ячейке находится стар-
ший  байт  числа,  а  в  следующей ячейке
младший байт этого числа.                
_______________________________