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Durango-X cartridge pinout
Connection to the computer
Durango-X uses a readily availbale 36-pin edge connector (2.54 mm pitch) as a cartridge port, supplying all necessary signals, plus some other for future expansion. Thus, the edge of the cartridge PCB can be inserted for a reliable connection.
Pinout
Cartridge connector as seen from above (component side, using KiCAD numbering):
| front pin # | front pin signal | back pin signal | back pin # |
|---|---|---|---|
| 35 | !RESET |
VCLK |
36 |
| 33 | D3 |
GND |
34 |
| 31 | D4 |
D2 |
32 |
| 29 | D5 |
D1 |
30 |
| 27 | D6 |
D0 |
28 |
| 25 | D7 |
A0 |
26 |
| 23 | !ROM_CS |
A1 |
24 |
| 21 | A10 |
A2 |
22 |
| 19 | !ROM_OE |
A3 |
20 |
| 17 | A11 |
A4 |
18 |
| 15 | A9 |
A5 |
16 |
| 13 | A8 |
A6 |
14 |
| 11 | A13 |
A7 |
12 |
| 9 | A14 |
A12 |
10 |
| 7 | +5 V |
!WE |
8 |
| 5 | KEY | KEY | 6 |
| 3 | !IOC |
AUDIO IN |
4 |
| 1 | !IRQ |
!NMI |
2 |
Note
Pins 5 & 6 have no connection and are designed as a key to prevent accidental reverse insertion of the cartridge. Cartridge PCBs must have a slot at this position, whereas the connector on the computer should have its corresponding pins removed and, if possible, with some filling inside.
Signal description
Signal direction is as seen from the computer's point of view:
| Signal | direction | Description |
|---|---|---|
+5 V, GND |
Out | Power supply from the computer. |
D0-D7 |
I/O | Data bus. |
A0-A14 |
Out | Address bus (A15 is missing but it's mostly the inverse of !ROM_CS) |
!RESET |
Out | Active-low reset. Cartridges cannot request a computer reset. |
VCLK |
Out | Main Phi 0 clock signal (1.536 MHz) |
!IRQ |
In | Active-low Interrupt ReQuest, must be an open collector signal from cartridge or, at least, use a diode with the anode on the connector pin. |
!NMI |
In | Non-Maskable Interrupt (edge-sensitive), must be open collector as the above one. |
!IOC |
Out | Active-low Cartridge I/O enable (addressed at $DFC0-$DFFF, VCLK-qualified), completely custom, just for decoding convenience. |
!WE |
Out | Active-low Write enable; not used for ROMs but useful for shadow RAM and I/O. VCLK-qualified for convenience. |
!ROM_CS |
Out | Active-low ROM Chip Select, nominally !A15 NAND !IO (excludes I/O area at $DF80-$DFFF) |
!ROM_OE |
Out | Active-low ROM Output enable, nominally VCLK NAND R!W (note it's VCLK-qualified) |
AUDIO IN |
In | For cartridges providing sound hardware, this pin is connected to the Audio mixer thru a diode. Analogue signals must provide a ~3.15 V DC bias and ~3.8 Vpp max. amplitude for optimum performance. |
RESET line
This is intended to be detected by some cartridges, either for resetting any additional hardware they may contain, or to switch between software inside a large ROM in a suitable multi-cartridge (under development). There is no way for the cartridge to reset the whole computer by itself!
Audio In
Since the built-in audio capabilities of Durango-X are quite limited, there is the option of including audio-generating circuitry inside a cartridge, mixing its audio output with the single-bit built-in device. Mostly designed with square wave generators in mind, it's possible to inject an analogue signal as long as the proper bias (~3.15 V) is supplied. In its simplest way, this could be achieved thru a voltage divider between the power pins -- a 3.3K resistor to +5V and a 5.6K one to ground could be a simple solution, with a suitable coupling capacitor (e.g. 10 µF) between the generator's output (as long as it supports load impedances below ~2 Kohm) and the divider.
Form factor
Although the current cartridges are intended to be used as bare PCBs, the preferred form factor for Durango cartridges is the same as used on Commodore 64 cartridges for convenience. Note the 36-pin PCB is narrower than the original's 44-pin, thus the edge connector must provide appropriate offset.