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 Snapshot date: 2024-01-15
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Generic Retro Computer Bus Definition

The expansion connector for GRC modules is a 2×25, 2.54mm spacing female header on the backplane and a corresponding right-angle male connector on each module. The following is the pin assignment of the GRC expansion connector.

Pin NumberSignal NameDescription
1 GND Ground
2 VCC +5V
3 nCS5 Chip select #5, active low
4 D7 Data bus 7, bidirection
5 nCS4 Chip select #4, active low
6 D6 Data bus 6, bidirection
7 nCS3 Chip select #3, active low
8 D5 Data bus 5, bidirection
9 nCS2 Chip select #2, active low
10 D4 Data bus 4, bidirection
11 nCS1 Chip select #1, active low
12 D3 Data bus 3, bidirection
13 nWRCF Compact flash write strobe, active low
14 D2 Data bus 2, bidirection
15 nRDCF Compact flash read strobe, active low
16 D1 Data bus 1, bidirection
17 nCSCF Compact flash chip select, active low
18 D0 Data bus 0, bidirection
19 nCSRAM RAM chip select
20 CPU Ctrl4 CPU-specific control line
21 nNMI Non-maskable interrupt
22 CPU Ctrl3 CPU-specific control line
23 nWAIT CPU wait, active low
24 nWR Write, active low
25 Bank3 Memory bank select, MSB
26 CPU Ctrl2 CPU-specific control line
27 Bank2 Memory bank select
28 CPU Ctrl1 CPU-specific control line
29 Bank1 Memory bank select
30 nIRQ Interrupt
31 Bank0 Memory bank select, LSB
32 nRESET System reset, active low
33 A15 Address line, MSB
34 CLK System clock
35 A14 Address line
36 A0 Address line, LSB
37 A13 Address line
38 A1 Address line
39 A12 Address line
40 A2 Address line
41 A11 Address line
42 A3 Address line
43 A10 Address line
44 A4 Address line
45 A9 Address line
46 A5 Address line
47 A8 Address line
48 A6 Address line
49 GND Ground
50 A7 Address line