Other device addresses are possible. Each device has its own address. Certain devices (like the Commodore 64 printer) provide a choice between two addresses for the convenience of the user.

The SECONDARY ADDRESS is to let the Commodore 64 transmit setup information to a device. For example, to OPEN a connection on the bus to the printer, and have it print in UPPER/LOWER case, use the following

   OPEN 1,4,7

• 1 is the logical file number (the number you PRINT# to),
• 4 is the ADDRESS of the printer, and
• 7 is the SECONDARY ADDRESS that tells the printer to go into UPPER/LOWER case mode.

There are 6 lines used in serial bus operations - input and 3 output. The 3 input lines bring data, control, and timing signals into the Commodore 64. The 3 output lines send data, control, and timing signals from the Commodore 64 to external devices on the serial bus.

SERIAL BUS PINOUTS

Pin	Type
1	/SERIAL SRQ IN
2	GND
3	SERIAL ATN OUT
4	SERIAL CLK IN/OUT
5	SERIAL DATA IN/OUT
6	/RESET