Commodore 1581 - Page 137

The 6-pin DIN connector looks like (from outside):
In detail, the 1581 serial bus supports the newer FAST serial com
munication as well as standard (SLOW) serial communication.
The important difference between the FAST serial bus and the
SLOW serial bus is the incorporation of the hardware controlled lines
for the CLOCK and DATA lines. Fast serial communication is transpar
ent to any peripheral connected to the serial bus that does not contain
the necessary hardware or software to talk at fast speed.
To remain compatible with the SLOW serial bus all bytes sent un
der attention are sent slow.
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