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 |
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