page@loral.UUCP (Dave Page) (02/26/85)
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)|-----------|-\
| >---<XXX>---o RS232 Txd
+---|+/
| |/
|
+5V o--<XXX>-+-<XXX>--o Gnd
5kohm 1kohm
100ohm 1kohm
|\
RS232 Rxd o-<XXX>--|-\
| >--+-<XXX>-->|--+--o |(B) & (C)
+---|+/ | |
| |/ | |
| | |
Gnd o--<XXX>-+-<XXX>---+ +--<XXX>-o Gnd
1kohm 10kohm 3kohm
Legend:
->|- or -|<- are 1N914 Diodes
-<XXX>- 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).