Atari ST

Keyboard Connector

I believe the following is applicable to all ST^F, ST^FM, and ST^E models.

The keyboard connects to the motherboard using an 8-pin female header.

Keyboard PCB	Connect to motherboard

Pin	Description
1	GND
2	KEY (not connected)
3	LED / Drive 0 Select
4	VCC +5V
5	TX
6	RX
7	RESET
8	GND

Sources:

• 1040ST Keyboard Schematic
• Atari STe 520/1040 Computer Field Service Manual

From Atari ST Internals by Abacus Software, chapter 2.1 The Keyboard:

The signal that the ACIA has received a byte is first sent over line 14 to the MFP 68901 which then generates an interrupt to the 68000. The clock frequency of 500KHz comes from GLUE. From this results the "odd" transfer rate of 7812.5 baud.