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Pinout

Using 96 position (3x32) DIN 41612 connectors; right angle male on expansion cards, vertical female on the backplane side. The management card uses a 48 position (3x16) DIN 41612 (C2) right angle male connector, with the corresponding vertical female on the backplane side.

CPU Board

The pinout of the CPU board’s expansion connector is documented on the CPU board expansion page.

Management Card

This provides power input to the rest of the backplane, and provides connectors for the mixed audio from the backplane.

  A B C
1 +5V +5V +5V
2 +5V +5V +5V
3 +5V +5V +5V
4 GND GND GND
5 +12V +12V +12V
6 GND GND GND
7   GND  
8   GND  
9   GND  

10

  GND  
11   GND  
12 /EXTRST GND  
13   GND I2C_IRQ
14 I2C_SCL GND I2C_SDA
15   GND  
16 SNDR GND SNDL

Any empty cells are not filled in are considered reserved for future use, and should be left unconnected.

Remarks

  1. SNDL/SNDR refers to mixed audio from all cards (CPU + expansion) in the system.
  2. EXTRST: when asserted, the CPU board (and with it, all peripherals on the backplane) are reset. This is equivalent to pushing the reset button on the CPU board, if it has one.

Peripheral

These connectors are provided by peripherals; they're 96-position, 3 row type C DIN 41612 connectors. They shall be right angle, male type.

  A B C
1 +5V GND +12V
2 +5V GND +12V
3 I2C_SCL1 /I2C_IRQ1 I2C_SDA1
4 GND GND GND
5 GND D8 D13
6 D9 D11 D15
7 D10 D14 D12
8 D7 D5 GND
9 D6 GND D3

10

GND D4 D1
11 D2 D0 GND
12 GND GND A22
13 A23 GND A19
14 GND A21 A17
15 A20 A15 A18
16 A13 A16 A12
17 A14 A10 GND
18 A11 GND A8
19 GND A9 A6
20 A7 A4 A2
21 A5 A3 A1
22 R/W /LDS /UDS
23 GND /DTACK /AS
24 CLK GND  
25 FC1 FC0 FC2
26      
27 /IRQ_IN /DETECT GND
28 /IRQ_OUT /BG /HALT2
29 /RESET2 /BR2 /BGACK2
30 /IACK /IRQ2 /BERR2
31 GND GND GND
32 SNDR GND SNDL

Remarks

  1. Pulled up to +5V by backplane
  2. These signals should be driven as open drain; they're pulled up by either the backplane or CPU board.
  3. If the card doesn't provide sound, tie SNDL/SNDR to ground through a 100kΩ resistor.
  4. Cards should tie /DETECT to GND so that the backplane can detect which slots are occupied, even if the card doesn't have anything on its I2C bus.

Interrupt Arbitration

Peripheral cards arbitrate interrupt priority in slot order. This works by means of a daisy-chained interrupt request line from each slot to the next. The first slot has the daisy chain input tied permanently high. Each peripheral outputs whether it has a pending interrupt on these pins, and then asserts the shared interrupt line. When an interrupt acknowledge cycle takes place, the peripheral with the highest priority – that is, whichever has an /IRQ_IN that's deasserted – responds.

When its interrupt conditions are cleared (from within its ISR,) it will deassert /IRQ_OUT and /IRQ. If there's a lower priority card requiring attention, the interrupt will fire again and it will respond. Otherwise, the processor returns to normal execution.

The /IRQ_IN pin on cards is pulled down to GND with a 1MΩ resistor on the backplane for all slots to prevent erroneous interrupt behavior if cards aren't inserted one after another in the backplane, e.g. the interrupt priority chain is broken. Cards can drive these pins either directly, or open drain, but in the latter case, it must provide the required pull up resistors. For open drain driving, a pull up value of at least 47kΩ is suggested.