Gnd

C H A P T E R 2

Hardware Modiﬁcations

Table 2-3 lists and describes the interface signals for the 40-pin segment of the connector.

Table 2-3Hard disk SCSI connector signal assignments: SCSI and power

Pin	Signal name	Description
1, 2	+5V logic	+5 V power supply
3, 4	Logic return	+5 V return
5, 7, 9, 11, 13,	GND	Ground
15, 19, 21, 23,
27, 31, 35
6	/DB0	Data bus bit 0
8	/DB1	Data bus bit 1
10	/DB2	Data bus bit 2
12	/DB3	Data bus bit 3
14	/DB4	Data bus bit 4
16	/DB5	Data bus bit 5
17	KEY	Not connected; used as connector key
18	/DB6	Data bus bit 6
20	/DB7	Data bus bit 7
22	/PARITY	Data bus parity
24	TERM PWR	Terminator power; pulls up termination resistors for
		all signal lines
25	/ATN	Attention indicator
26	/BSY	Busy signal
28	/ACK	Acknowledge (handshake signal); asserted in
		response to a request for access (/REQ)
29	/RST	SCSI bus reset
30	/MSG	Message phase
32	/SEL	SCSI select
33	/I/O	Controls the direction of data movement: when this
		signal is low, data is output from the disk drive;
		when it is high, data is input
34	/C/D	Indicates whether data or control signals are on the
		SCSI bus: when this signal is low, data is on the bus;
		when it is high, control signals are on the bus
36	/REQ	Access request; the CPU asserts this signal to
		request access to the hard disk
37, 38	MOTOR RET	Return for +5 V power supply for motor
39, 40	+5V MOTOR	+5 V power supply for the motor

12	200 MB Hard Disk Drive