I/O Extension For Amiga 500

EE JULY/AUGUST 1988 The Commodore Amiga is claimed to be a computer with plenty of facilities for extension circuits. The model 500, for instance, comes with no fewer than twelve connectors and sockets. There are, however, awkward constraints to the practical use of all these extension facilities. The SERIAL CONNECTOR 1S cumbersome to use with TTL circuits because of the +12 V logic levels on it. The use of the 86-PIN CONNECTOR on the machine is complex and risky because of the unbuffered connection to many internal signals. The one remaining op- tion is the PARALLEL CONNECTOR, which can be extended to a maximum of 56 I/O lines as shown here, with the possi- bility to realize a bidirectional port. The circuit was designed and built for the Amiga 500 computer. It is likely to work equally well on models 1000 and 2000, but this has not been tested in practice. Output lines BUSY, P-OUT and SEL on the PARALLEL CONNECTOR can be pro- 5V I/O EXTENSION FOR AMIGA 500 grammed to supply a 3-...