RS-232C Interface for C64/C128

Below diagram shows one of the simplest method to build an adaptor to hook an external modem to a C64. I guess you can find the IC 7404 easily. With a C128 it can go up to 9600 bps, but for a stock C64 it requires very special tricks to access the limiting speed of 2400 bps.

The schematics belongs to Walter Wickersham ( shadow@connected.com ).

user port                               RS232 DB25   DB9   description
---------                               ----------   ---   -----------

  A & N------------------------+-----------1 & 7      5      ground
                        _____  I 
  B & C----------------[2   7]-+      
                       [     ]    
    M------------------[3   1]-------------3          2      rx
                       [     ]
    2------------------[14  4]-------------2          3      tx
                       [_____]

Part List
7404 IC (you can easily find it)
DB25 male connector (or DB9 male)
User Port connector
2m. 2 line shielded cable. (you don't need this if your modem has the cable)

Connector Views (looking at the front faces)

user port                  DB25                              DB9
                                                1 1 1 1       
                  1 1 1       1 2 3 4 5 6 7 8 9 0 1 2 3         1 2 3 4 5
1 2 3 4 5 6 7 8 9 0 1 2    \-----------------------------/   \-------------/
- - - - - - - - - - - -     \ . . . . . . . . . . . . . /     \ . . . . . /
- - - - - - - - - - - -      \ . . . . . . . . . . . . /       \ . . . . /
A B C D E F H J K L M N       -------------------------         ---------
                               1 1 1 1 1 1 2 2 2 2 2 2           6 7 8 9
                               4 5 6 7 8 9 0 1 2 3 4 5

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