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From: prindle@nadc
Newsgroups: net.micro.cbm
Subject: RS-232 adapter circuit schematic
Message-ID: <1685@caip.RUTGERS.EDU>
Date: Thu, 3-Apr-86 06:26:24 EST
Article-I.D.: caip.1685
Posted: Thu Apr  3 06:26:24 1986
Date-Received: Sat, 5-Apr-86 10:59:45 EST
Sender: daemon@caip.RUTGERS.EDU
Organization: Rutgers Univ., New Brunswick, N.J.
Lines: 61

From: prindle@NADC


I found it!
Here is the schematic for the interface I've used for several years.  Of course,
there is a new chip available from Maxim Integrated Products called the
MAX232 which will produce true +/- 10V RS-232 from a +5V supply and TTL inputs,
but you won't be able to waltz into your Radio Shack and get one for a year or
so anyway, so......

(Incidentally, this will fit on a 1 inch square PC board)
Frank Prindle
Prindle@NADC.arpa
--------------------------------------------------------------------------------


    Commodore 64 to RS-232 Modem Interface (if modem will accept TTL levels)
    ------------------------------------------------------------------------

User Port Pin                                                  Modem Pin (DB-25)
-------------                                                  -----------------


  +5V   2>-------->+5V

                                   +5V
                                    ^
                    2K              |
             -----/\/\/\-------------
             |                      |   -------------------------<2   BA  Xmit
             |      10K         |<---   |                                 Data
XMIT    M>--------/\/\/\--------|       |     1K
DATA                            |-----------/\/\/\---
                           2N2907A (PNP)            |
                                                    |
                                                  -----
                                   ^                -
                             5K    |
                     ------/\/\/\---
                     |
                     | 2N2222A (NPN)
RECV    B>---------------|                    5K
DATA         |           |------------------/\/\/\---------------<3   BB  Recv.
        C>----     ----<-|         |                                      Data
                   |          |    |
                   |--------->|-----
                   |          |
                 -----   AOD (Any Old Diode)
                  ---
                   -


GND     N>-------------------------------------------------------<7   AB  Signal
                                       |                                  Ground
                                     -----
                                      --- 
                                       -  

Note:  This circuit is not particularly sensitive to transistor type - almost
       anything should work at this speed - the types given are representative
       of their type and should be available at Radio Shack.