# Apple Macintosh Portable ROM Expansion

50 PIN UNKNOWN CONNECTOR

Pin | Name | Description
--- | --- | ---
1 | +5V | +5 VDC
2 | A1 | Address bit 1
3 | A2 | Address bit 2
4 | A3 | Address bit 3
5 | A4 | Address bit 4
6 | A5 | Address bit 5
7 | A6 | Address bit 6
8 | A7 | Address bit 7
9 | A8 | Address bit 8
10 | A9 | Address bit 9
11 | A10 | Address bit 10
12 | A11 | Address bit 11
13 | A12 | Address bit 12
14 | A13 | Address bit 13
15 | A14 | Address bit 14
16 | A15 | Address bit 15
17 | A16 | Address bit 16
18 | A17 | Address bit 17
19 | A18 | Address bit 18
20 | A19 | Address bit 19
21 | A20 | Address bit 20
22 | A21 | Address bit 21
23 | A22 | Address bit 22
24 | A23 | Address bit 23
25 | GND | Ground
26 | GND | Ground
27 | /DTACK | Data Transfer Acknowledge
28 | /AS | Address Strobe
29 | /ROM_CS | ROM Chip Select
30 | 16M | 16 MHz Clock
31 | /EXT_DTACK | External Data Transfer Acknowledge
32 | /DELAY_CS |
33 | D0 | Data bit 0
34 | D1 | Data bit 1
35 | D2 | Data bit 2
36 | D3 | Data bit 3
37 | D4 | Data bit 4
38 | D5 | Data bit 5
39 | D6 | Data bit 6
40 | D7 | Data bit 7
41 | D8 | Data bit 8
42 | D9 | Data bit 9
43 | D10 | Data bit 10
44 | D11 | Data bit 11
45 | D12 | Data bit 12
46 | D13 | Data bit 13
47 | D14 | Data bit 14
48 | D15 | Data bit 15
49 | +5V | +5 VDC
50 | +5V | +5 VDC

## D0-D15

Unbuffered data bus, bits 0 through 15

## A1-A23

Unbuffered 68HC000 address bus, bits 1 through 23

## 16M

16 MHz system clock

## /EXT.DTACK

External data transfer acknowledge that disables main system /DTACK.

## /AS

68HC000 Address strobe

## /DTACK

Data transfer acknowledge, /DTACK input to 68HC000.

## /DELAY_CS

This signal is generated by the addressing PAL and is used to put the ROM board into the idle mode by inserting multiple wait states.

## /ROM_CS

Permanent ROM chip select signal. Selects in range $90 0000 through $9F FFFF.

Contributor: Joakim Ögren

Source:
Technote HW13: Macintosh Portable ROM Expansion at Apple Technical Notes

Copyright © The Hardware Book Team 1996-2001.
May be copied and redistributed, partially or in whole, as appropriate.
Document last modified: 2000-07-09