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

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Apple 250 manual Gnd