Apple LC520 Specifications download pdf (Page 23)

CHAPTER 1

Introduction

SCSI Bus 11

The Macintosh LC 520 computer includes a new feature that automatically provides the

proper termination when no external device is connected, that is, when the SCSI bus ends

at the external connector. When no external device is connected, special circuitry connects

the bus to a terminator on the logic board near the external connector. When one or more

external SCSI devices are connected, the circuitry detects the external termination during

system reset and disconnects the termination on the logic board.

Table 1-2 Pin assignments for the internal and external SCSI connectors

Internal

(50-pin)

External

(25-pin) Signal name

2 8 /DB0

4 21 /DB1

6 22 /DB2

8 10 /DB3

10 23 /DB4

12 11 /DB5

14 12 /DB6

16 13 /DB7

18 20 /DBP

20, 22, 24, 28,

30, and 34

– n.c.

26 25 TPWR

32 17 /ATN

36 6 /BSY

38 5 /ACK

40 4 /RST

42 2 /MSG

44 19 /SEL

46 15 /C/D

48 1 /REQ

50 3 /I/O

All odd pins

(25 total)

7, 9, 14, 16,

18, and 24

GND

1 2 ... 18 19 20 21 22 23 24 25 26 27 28 ... 73 74

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Apple LC520 Specifications Page 23