Move #04 17 апреля 1997

Железо

Iron - whose computer is a brand name.

                  IRON

(C) Ars MDM 249-97-53


   Quite often users Speccy arguing about whose computer is 
"more brand "that is" two-field machine "

etc. If you are interested in this topic, then
I advise to review the information "Inforkoma" on these issues.

                                   Ars.


   Z80 microprocessor can serve
address space in the 64K. In the standard
computer, it is distributed as follows:

           # FFFF

           ····· RAM

           # 8000 32K

           # 7FFF

           ····· RAM

           # 4000 16K

           # 3FFF

           ····· ROM

           # 0000 16K

In the lower addresses from # 0000 to # 3FFF ROM is 16K, which 
contains the operating Spectrum system. Memory addresses

# 4000 to # 7FFF performed on the 8 chips
Dynamic memory DRAM type 4116 with the organization 16Kx1. 
Domestic analog chip is 565PY3 or 565PY6 (the same but one 
source of supply). Additional memory to 32K addresses # 8000 to 
# FFFF is represented by 8 DRAM chips 64Kx1, which (all the 
same), rejected one of the halves - left, right, top or bottom. 
Our counterpart is the "half" chips 565PY5 labeled 565PY5D1 or 
565PY5D2. 

   In the firm Spectrum, as is known,
display controller is executed on a single LSI -
programmable logic array, or ULA
Uncomitted Logic Array. Cunning Circuits
type ULA was that, the manufacturer produced them in an 
unfinished form, ie as semi-finished, and then some

"Secret" shop it a bit being finalized ("sewed") under the 
requirements of the customer - Sinclair Research Ltd. Sir Clive 
Sinclair was forced to resort to such method of protecting your 
computer is instructed bitter experience with my previous 
machine ZX-81, which was immediately pirated

replicated across Europe. I must say that this protection has 
fulfilled its role brilliantly. Was not one year, until learned 
to emulate this chip using "Shallow logic." In homemade 
computers function ULA performs "rassypuha" from 20-40

chips, many different versions of the Spectrum is building a 
display controller and the number of chips, spent for him. 

   Memory Spectrum Display
located in addresses: # 4000 - # 57FF - Memory of the screen, # 
5800 - # 5AFF - Memory attributes. Every 20 ms Controller

display hardware properly reads the information from this area 
for regeneration images on the display screen, and for

each line of treatment in this area
occurs 64 times: 32 times read on
8-point line (consisting of 256 points)
alternating with 32-fold reading familiarity attributes, which 
include the this line. It is clear that during these

reads the microprocessor can not access memory chips, which are 
display memory. In the original machine this conflict is 
resolved as follows: if at the time of a hardware refresh on 
the screen display processor executing the program, will 
address these chips, then it no longer served the hardware 
clock. This, of course, slows down performance Programmes at, 
but not very strongly, because Firstly, do not slow down with 
"top" 32K of memory that are physically performed on

other chips, and secondly, the processor
"Free" work with "lower" 16K, referring to the Spectrum ROM, 
and, thirdly, he has the opportunity to work with on-screen 
memory area, because regeneration of the image is uneven, as 
shown on the diagram:


Reverse Border February 1
turn on | c

                 ~ · ·
Human Resources | a b a b


            Border Check

   c | move on
· · ~

      a b | rows

Work processor is suspended only while circulation at the moment
a) and b), when a) - is read
a byte buffer of the screen, b) - read bytes attribute 
familiarity. All other times - during the retrace frames, by 
rows, while the output curbs at the top, left and right sides 
nizhey screen, as well as within the basic framework

image at time c) the processor runs without any restrictions.

   From homemade Spectrum fullest replicate the ideology of 
corporate computer those that use separate memory. In variants 
with a common field of memory chips used 64Kx1, the lower 16K 
of which as it were "shadowed" Rom. Using the general field of 
memory reduces the total number of chips for 12-15 buildings, 
reduce consumption of a computer, its size, ie

has undoubted advantages. Complexity is here is that, to 
preserve the old speed of the program have to increase the 
frequency of recourse to memory, which increases the demands on 
the speed of memory chips, they agreed with other chips, etc. 
Processor in such options shall be suspended or strokes or stop 
using the signal WAIT. 

   It should also be noted that the firm
'Sinclair 128 +' is also made under the scheme made under the 
scheme with the general field of memory, and the first years 
after its appearance on the market users often noted some 
incompatibility of programs written previously for 'Spectrum 
16K' and 'Spectrum 48K', but programs written later, programmers

apparently took into account the architecture of the 128 th 
and, therefore, incompatibility of software in nearly

face is not necessary.