PX4 System Bus Interface

50-pin IDC connector (male)

Location: Left hand edge of the machine, with a small clip on cover. This is where RAM expansion modules and similar devices are attached.

[Image of connector later]
Description: 50 pin flat connector with two rows of pins, with the notches placed at the bottom, pin 1 is the bottom left hand pin, and pin 2 is above it. pin 49 is bottom right, with pin 50 being top right.

Pin No. Symbol I/O Signal Name
1 VCH P/S Battery charger line
2 VB1 P/S Battery power
3 VB2 P/S Battery power
4 VBK P/S Battery power
5 GND - Signal ground
6 VL P/S Power for logics
7 DB7 TTL Data 7
14 DB0 TTL Data 0
15 !MEN In Internal Memory Enable
16 !INTE In External interrupt
17 !WAIT In Z-80 wait
18 PON Out Power ON
19 !CLK Out Z-80 main clock
20 BUAK Out Bus acknowledge
21 !RD Out Z-80 data read
22 !IORQ Out Z-80 data request
23 !WR Out Z-80 data write
24 !MRQ Out Z-80 memory request
25 !HLTA Out Halt acknowledge
26 !BURQ In Z-80 bus request
27 CG - Protective Ground
28 CG - Protective Ground
29 !RS Out System reset
30 !M1 Out Z-80 machine cycle 1
31 AB0 Out Address 0
46 AB15 Out Address 15
47 OFF Out Gate array control at power switching
48 DW Out Expansion D-RAM RF control signal
49 DCAS Out Expansion D-RAM RF control signal
50 !RSI In Reset input
NOTE: Use CMOS ICs for the circuit to be connected to this interface.

NB: As i cant draw a line over the top of things easily in html, i have used the ! symbol infront of a signals symbol to indicate it is an inverse one.

All signal directions as viewed from PX-4