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C64 RS232 Schematic [message #112179] Mon, 16 September 2013 13:40
Anonymous
Karma:
Originally posted by: page@loral.UUCP (Dave Page)
Message-ID: <795@loral.UUCP>
Date: Tue, 26-Feb-85 14:00:42 EST
Article-I.D.: loral.795
Posted: Tue Feb 26 14:00:42 1985
Date-Received: Fri, 1-Mar-85 08:23:08 EST
Distribution: net
Organization: Loral Instrumentation, San Diego
Lines: 80



	Well here is the RS232 Interface that I mentioned some months
	ago. The first thing that you will notice is that it uses a
	charge pump to supply the +/- supplies required for true RS232.
	If you find that you have to tune a few parameters in order to
	clean up the supply levels it wouldn't suprise me. If done right
	this project should cost well less than $10. Good Luck!
 
			Dave Page
 
				RS232 Interface 
 
                 +- 9A
                 |                                 
          (11)|--+--->|---+---o +9V                
                          |                                         
          (10)|--+--->|---+-|(-o Gnd               
                 |                                 
                 +- 9B   
                                                                   
                9A--|<---+--|<---+--o -9V 
                         |       |
                         +-)|-+  +-)|-o Gnd 
                              |
                9B------------+ 
 
            (2)|------o +5V
 
      (N) & (A)|------o Gnd
 
                          100ohm 
                   |\
    (M)|-----------|-\
                   |  >------o RS232 Txd
               +---|+/
               |   |/ 
               | 
  +5V o---+---o Gnd 
         5kohm   1kohm 
                                                                    
            100ohm         1kohm 
                   |\
RS232 Rxd o---|-\
                   |  >--+--->|--+--o |(B) & (C) 
               +---|+/   |            | 
               |   |/    |            |
               |         |            |
  Gnd o---+----+            +---o Gnd 
         1kohm   10kohm                  3kohm 
                                                                    
 
 
    Legend:
 
    ->|- or -|<-    are 1N914 Diodes
 
    --         are 1/4W resistors
 
    -)|- or -|(-    are 35MFD Capacitors
 
    (XX)            are C64 User Port Pin Assignments
 
      |\
    o-|-\
      |  >---o      are LM741 op amps or equivelent 
    o-|+/   
      |/    
 
 
       The User is expected to know where +/- supplies attach to
      the opamp being used and to determine the pinout. All resistor
      and capacitor values are nominal and may require fine tuning.
      The prototype model of this circuit was found to run fine with
      both our VAX at 75ft run and my 1200baud modem at 40ft. If
      more than 3 line handshake is desired the charge pump should
      be modified for full wave operation and the approprate I/O
      circuit wired in (either transmitt or receive). 
 
 
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