Tower Bus
The physical bus is comprised of a small passive PCB backplane which acts as a rigid flying bus (in Eurorack terms). For prototyping this could be substituted with IDC ribbon cables even. The long edge of each card then has 2x40 (or 2x 2x20) DIL signal and 2x8 DIL power header. These will be placed apart from each other which makes the connector asymmetric meaning a card cannot be plugged in backwards.
Devices which support audio additionally can expose out a 1x4 SIL header to be used for internal audio routing (say to a Mixer card).
Signal Summary
- +3.3V logic levels
- Cards must regulate 3.3V from 5V
- Address Pins: A18-A00
- Data Pins: D7-D0
- Device Select Pins: !DS7-DS0
- Other Pins: !R, !W, !RESET, !IRQ, AUX, Clock
- Checkerboard Grounds In Between Most Signals
- Power (+5V, -12V, +12V, Extra Grounds)
- Optional Audio Header: L, R, GND
Pinout
Signal Header
40-pin dual row (DIL) header
This is now wrong (due to A18 vs A19) but try to keep 40-pin header
| Col | Row 1 | Row 0 |
|---|---|---|
| 00 | A18 | GND |
| 01 | GND | A17 |
| 02 | A16 | GND |
| 03 | GND | A15 |
| 04 | A14 | GND |
| 05 | GND | A13 |
| 06 | A12 | GND |
| 07 | GND | A11 |
| 08 | A10 | GND |
| 09 | GND | A09 |
| 10 | A08 | GND |
| 11 | GND | A07 |
| 12 | A06 | GND |
| 13 | GND | A05 |
| 14 | A04 | GND |
| 15 | GND | A03 |
| 16 | A02 | GND |
| 17 | GND | A01 |
| 18 | A00 | GND |
| 19 | GND | D7 |
| 20 | D6 | GND |
| 21 | GND | D5 |
| 22 | D4 | GND |
| 23 | GND | D3 |
| 24 | D2 | GND |
| 25 | GND | D1 |
| 26 | D0 | GND |
| 27 | GND | CLK |
| 28 | AUX | GND |
| 29 | GND | !R |
| 30 | !W | GND |
| 31 | !IRQ | !RES |
| 32 | GND | !DS7 |
| 33 | !DS6 | GND |
| 34 | GND | !DS5 |
| 35 | !DS4 | GND |
| 36 | GND | !DS3 |
| 37 | !DS2 | GND |
| 38 | GND | !DS1 |
| 39 | !DS0 | GND |
Power Header
2x8 DIL Header
| Col | Row 1 | Row 0 |
|---|---|---|
| 00 | GND | +5V |
| 01 | GND | +5V |
| 02 | GND | +5V |
| 03 | GND | +5V |
| 04 | GND | +12V |
| 05 | GND | +12V |
| 06 | GND | -12V |
| 07 | GND | -12V |
Audio Pinout
4-pin SIL header
| Row 3 | Row 2 | Row 1 | Row 0 |
|---|---|---|---|
| L | GND | GND | R |
References
- https://resources.altium.com/p/complete-guide-to-selecting-board-to-board-connectors
- https://www.lcsc.com/product-detail/C41432069.html?spm=wm.fly.bg.0.xh&lcsc_vid=QVJbAVBRTlVYUAEEFlJWVlVTFVkLXl1VRFJYVQcHRVMxVlNeRFJYUFVSTlFaUzsOAxUeFF5JWBYZEEoKFBINSQcJGk4eFQsCAgIaSgADAwAHC0slQlJdVFBXTk8GEwkK