Crazy hands - RS232 port.

                                         
                                         
DEVELOPMENT OF INTERFACING DEVICES
for personal computer   
IBM PC type                    
                                         
  Yu.V.Novikov                            
  O.A. Kalashnikov                         
  S.E.Gulyaev                             
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              Chapter 4                    
                                         
     DEVELOPMENT OF INTERFACING DEVICES     
             FOR RS-232С                 
                                         
4.2 Circuit design of level converters 
                                         
  Depending on the requirements, presenting
adaptable to the designed system, transformed
level summoners can be performed by self-
in different ways.              
 So, when transmission and reception are required
just one pair of signals ( TxD and
RxD), and it is desirable to be able
quickly restore functionality
system in case of failure,
you can use a transmitter made
on discrete components (Fig. 4.2). 
  The operation of the scheme hardly requires
tsa in the comments, and transistors KTZ15 and
KTZb1, as a rule,are indispensable
a significant attribute of any laboratory.        
  For the simplest signal receiver
no research port required at all
no additional circuits other than input ones
level limiters and inverter, but that's all
it’s not bad if the receiver has
some hysteresis. Quite suitable
The diagram for use is shown on
fig. 4.3.                               
  However, it often happens that the application
discrete elements is undesirable
essential, and if, in addition, it is required
presence of more than two signals in sequence
body interface, then the best solution
may be the use of specialized
interface integrated microphones
level converter circuits, for example
IFC1488 (KPSS9IP19) and IFC1489    
(KPSS9IP20), presented in Fig. 4.4
and rice 4.5.                             
  The outputs of the IFC1488 chip have after-
additionally included resistors with a nominal value
300 ohms and provide bipolar levels
Uout +/- 6V. By information inputs
(RxD) the microcircuit has hysteresis,
whose position is determined by the voltage
voltage supplied through the current-limiting
resistor to terminals "g". Allowed
Leave these pins unconnected.   
  Microcircuits KPSS9IP19 and IP20 are produced
currently the Belarusian association
We eat "Integral" (Minsk).           
  From the pointdigital developer perspective
equipment, an obvious disadvantage of both
types of level converters are
the need to have a source of dual power
polar supply voltage +/- 12 V.    
                                         
  Do without additional sources
nutrition is possible by using specially
interfaces developed for this purpose
microcircuits A wide range of such crystals
fishing is produced by the well-known company MAXIM. 
  They contain a voltage converter
+5 V voltage +10 V (generator + mind-
voltage carrier), inverter (converter)
developing voltage +10 V to -10) and
the signal level converters themselves
catching the serial interface.
Most of them require additional
elements (requires external condensation -
tori ) , which is not excessive pla-
that for the advantages of their use.      
                                         
  In conclusion of the review of converters
level it seems useful to mention
about another scheme that can have
assistance in case you need to provide
make communication at a considerable distance
serviced object from a computer with
saved as an I/O port
standard serial interface
sa. This is a circuit (Fig. 4.9) converting
RS-232С - "current loop 20 mA",
carrying outbesides galvanic
decoupling the computer from the control object
nia.                                    
  Note that galvanic isolation
can be extremely necessary no matter how
be a significant distance between any
objects connected electrically
cable  In such situations it is known
quite numerous cases of exit from
building computers that were grounded
us, but were in different rooms.
Measurements of currents flowing at zero
wire of connecting cables, give ta-
some crazy values like 2-3 A,
despite the fact that both ends of this pro-
The water seems to be grounded.                
  This scheme (Fig. 4.9) provided
communication between a computer and a remote controller
with a cable length of about 2 km at speed
38400 bps. Obviously for bidirectional
line communication receiving and transmitting parts
must be connected to both ends of the cable
whitewash                                   
                                         
 * Numbering of chapters and figures as in the source
nick.                                   
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Pantera>In the magazine application you will find  
three screen files representing
circuit diagram of RS232. And also the circuit diagram
new mikruhi related to the port.