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CHAPTER 2
Hardware Modifications
12
200 MB Hard Disk Drive
Table 2-3 lists and describes the interface signals for the 40-pin segment of the connector.
Table 2-3
Hard 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,
15, 19, 21, 23,
27, 31, 35
GND Ground
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