This section contains bus signal charts and backplane layout illustrations.
Cardcage slot numbers are stamped, printed, or labeled on the sheet metal near the card ejectors. VMEbus backplane jumpers are silk-screened on the cardcage as Px00, Px01, Px02, Px03, and Px04 or Jx00, Jx01, Jx02, Jx03, and Jx04; where x represents the card slot number.
These jumpers control VMEbus signals BUS GRANT 0-3 IN (BG0-3IN) to BUS GRANT 0-3 OUT (BG0-3 OUT), and INTERRUPT ACKNOWLEDGE IN (IACKIN) to INTERRUPT ACKNOWLEDGE OUT (IACKOUT). The VMEbus signals are referred to as BG0, BG1, BG2, BG3, and IACK in this section.
| LABEL | SIGNAL | ABBREVIATION |
| Jxx0 Pxx0 | BUS GRANT 0 | BG0 |
| Jxx1 Pxx1 | BUS GRANT 0 | B01 |
| Jxx2 Pxx2 | BUS GRANT 0 | BG2 |
| Jxx3 Pxx3 | BUS GRANT 0 | BG3 |
| Jxx4 Pxx4 | INTERRUPT ACKNOWLEDGE |
IACK |
The VMEbus consists of signals on J1/P1 Row A, J1/P1 Row B, J1/P1 Row C, and J2/P2 Row B.
The Sun P2 Bus consists of signals on J2/P2 Row A, J2/P2 Row C, and J3/P3 Row B.
| PIN | ROW A | ROW B | ROW C |
| 1 | D00 | BBSY* | D08 |
| 2 | D01 | BCLR* | D09 |
| 3 | D02 | ACFAIL* | D10 |
| 4 | D03 | BG0IN* | D11 |
| 5 | D04 | BG0OUT* | D12 |
| 6 | D05 | BG1IN* | D13 |
| 7 | D06 | BG1OUT* | D14 |
| 8 | D07 | BG2IN* | D15 |
| 9 | GND | BG2OUT* | GND |
| 10 | SYSCLK | BG3IN* | SYSFAIL* |
| 11 | GND | BG3OUT* | BERR* |
| 12 | DS1* | BR0* | SYSRESET* |
| 13 | DS0* | BR1* | LWORD* |
| 14 | WRITE* | BR2* | AM5 |
| 15 | GND | BR3* | A23 |
| 16 | DTACK* | AM0 | A22 |
| 17 | GND | AM1 | A21 |
| 18 | AS* | AM2 | A20 |
| 19 | GND | AM3 | A19 |
| 20 | IACK* | GND | A18 |
| 21 | IACKIN | SERCLK | A17 |
| 22 | IACKOUT* | SERDAT | A16 |
| 23 | AM4 | GND | A15 |
| 24 | A07 | IRQ7* | A14 |
| 25 | A06 | IRQ6* | A13 |
| 26 | A05 | IRQ5* | A12 |
| 27 | A04 | IRQ4* | A11 |
| 28 | A03 | IRQ3* | A10 |
| 29 | A02 | IRQ2* | A09 |
| 30 | A01 | IRQ1* | A08 |
| 31 | -12V | +5VSTDBY | +12V |
| 32 | +5V | +5V | +5V |
| PIN | ROW A | ROW B | ROW C |
| 1 | User Defined | +5 | User Defined |
| 2 | User Defined | GND | User Defined |
| 3 | User Defined | RESERVED | User Defined |
| 4 | User Defined | A24 | User Defined |
| 5 | User Defined | A25 | User Defined |
| 6 | User Defined | A26 | User Defined |
| 7 | User Defined | A27 | User Defined |
| 8 | User Defined | A28 | User Defined |
| 9 | User Defined | A29 | User Defined |
| 10 | User Defined | A30 | User Defined |
| 11 | User Defined | A31 | User Defined |
| 12 | User Defined | GND | User Defined |
| 13 | User Defined | +5 | User Defined |
| 14 | User Defined | D16 | User Defined |
| 15 | User Defined | D17 | User Defined |
| 16 | User Defined | D18 | User Defined |
| 17 | User Defined | D19 | User Defined |
| 18 | User Defined | D20 | User Defined |
| 19 | User Defined | D21 | User Defined |
| 20 | User Defined | D22 | User Defined |
| 21 | User Defined | D23 | User Defined |
| 22 | User Defined | GND | User Defined |
| 23 | User Defined | D24 | User Defined |
| 24 | User Defined | D25 | User Defined |
| 25 | User Defined | D26 | User Defined |
| 26 | User Defined | D27 | User Defined |
| 27 | User Defined | D28 | User Defined |
| 28 | User Defined | D29 | User Defined |
| 29 | User Defined | D30 | User Defined |
| 30 | User Defined | D31 | User Defined |
| 31 | User Defined | GND | User Defined |
| 32 | User Defined | +5V | User Defined |
| PIN | ROW A | ROW B | ROW C |
| 1 | +5V | User Defined | GND |
| 2 | +5V | User Defined | GND |
| 3 | +5V | User Defined | GND |
| 4 | +5V | User Defined | GND |
| 5 | +5V | User Defined | GND |
| 6 | +5V | User Defined | GND |
| 7 | +5V | User Defined | GND |
| 8 | +5V | User Defined | GND |
| 9 | +5V | User Defined | GND |
| 10 | +5V | User Defined | GND |
| 11 | +5V | User Defined | GND |
| 12 | +5V | User Defined | GND |
| 13 | +5V | User Defined | GND |
| 14 | +5V | User Defined | GND |
| 15 | +5V | User Defined | GND |
| 16 | +5V | User Defined | GND |
| 17 | +5V | User Defined | GND |
| 18 | +5V | User Defined | GND |
| 19 | +5V | User Defined | GND |
| 20 | +5V | User Defined | GND |
| 21 | +5V | User Defined | GND |
| 22 | +5V | User Defined | GND |
| 23 | +5V | User Defined | GND |
| 24 | +5V | User Defined | GND |
| 25 | +5V | User Defined | GND |
| 26 | +12V | User Defined | +12V |
| 27 | +12V | User Defined | +12V |
| 28 | -12V | User Defined | -12V |
| 29 | -12V | User Defined | -12V |
| 30 | -5V | User Defined | -5V |
| 31 | -5V | User Defined | -5V |
| 32 | -5V | User Defined | -5V |
Pressfit Backplane production began in June 1987. Solderless contacts are machine pressed into plated-through holes on printed circuit boards. Component leads installed into the solderless contacts are held in place by a tapered entry, multi-finger contact design.

Memory board options plug into connector J3, Slots 4 and 5, on the 501-1354 backplane. The Sun P2 bus connects Slots 1, 4, and 5 as shown below.
| J102 Row A | Connects to J403 Row A and J503 Row A |
| J102 Row C | Connects to J403 Row C and J503 Row C |
| J103 Row B | Connects to J403 Row B and J503 Row B |
Cardcage Slots 4 and 5 share a private bus that connects signals between J2/P2, Row A and J2/P2, Row C. These slots are used with 6U VMEbus boards.
The function of the backplane jumpers is shown below.
| JUMPER | CONNECTS |
| P2xx | BG0-3IN to BG0-3Out and IACKIN to IACKOUT on slot 2 |
| P3xx | BG0-3IN to BG0-3Out and IACKIN to IACKOUT on slot 3 |
| P4xx | BG0-3IN to BG0-3Out and IACKIN to IACKOUT on slot 4 |
The Sun P2 bus connects cardcage Slots 1 through 7 to each other, and cardcage Slots 10, 11, and 12 to each other.
In addition to the Sun P2 bus and the VMEbus, the 12-slot backplane has a private Internal bus that connects Slots 1, 2, and 3 as shown below.
| J101 Row A | Connects to J201 Row A and J301 Row A |
| J101 Row B | Connects to J201 Row B and J301 Row B |
| J101 Row C | Connects to J201 Row C and J301 Row C |
| J102 Row B | Connects to J202 Row B and J302 Row B |
J1/P1, Rows A, B, and C, on Slots 1, 2, and 3 are not connected to the VMEbus. Boards that use the VMEbus cannot be used in Slots 1, 2, or 3. J2/P2, Row B, is connected between Slots 1 through 7.
The 501-1439 Backplane terminates J2/P2, Row C, Pins 75 and 96 with a 40.2 Ohm resistor and a 47pf capacitor.
The 501-1598 and 501-1832 Backplanes terminate J2/P2, Row C, Pins 75 and 96 with a 200 Ohm resistor. Termination is jumper selectable.
The Sun 4400 CPU is not supported in the 501-1439 Backplane.
The function of the backplane jumpers is shown below.
| JUMPER | CONNECTS |
| J4xx | BG0-3IN to BG0-3Out and IACKIN to IACKOUT on slot 4 |
| J5xx | BG0-3IN to BG0-3Out and IACKIN to IACKOUT on slot 5 |
| J6xx | BG0-3IN to BG0-3Out and IACKIN to IACKOUT on slot 6 |
| J7xx | BG0-3IN to BG0-3Out and IACKIN to IACKOUT on slot 7 |
| J8xx | BG0-3IN to BG0-3Out and IACKIN to IACKOUT on slot 8 |
| J9xx | BG0-3IN to BG0-3Out and IACKIN to IACKOUT on slot 9 |
| J10xx | BG0-3IN to BG0-3Out and IACKIN to IACKOUT on slot 10 |
| J11xx | BG0-3IN to BG0-3Out and IACKIN to IACKOUT on slot 11 |
| J12xx | BG0-3IN to BG0-3Out and IACKIN to IACKOUT on slot 12 |
The Sun P2 bus connects cardcage Slots 1 through 7 to each other, cardcage Slots 11 and 12 to each other, and cardcage Slots 13, 14, and 15 to each other.
In addition to the Sun P2 bus and the VMEbus, the 16-slot backplane private internal bus connects Slots 1, 2, and 3 as shown below.
| J101 Row A | Connects to J201 Row A and J301 Row A |
| J101 Row B | Connects to J201 Row B and J301 Row B |
| J101 Row C | Connects to J201 Row C and J301 Row C |
| J102 Row B | Connects to J202 Row B and J302 Row B |
J1/P1 Rows A, B, and C on Slots 1, 2, and 3 are not connected to the VMEbus. Boards that use the VMEbus cannot be used in Slots 1, 2, or 3. J2/P2, Row B, is connected between Slots 1 through 7.
The 501-1498 Backplane must be 501-1498-02 or greater when used with the Sun 4400 CPU.
The function of the backplane jumpers is shown below.
| JUMPER | CONNECTS |
| J2xx | BG0-3IN to BG0-3Out and IACKIN to IACKOUT on slot 2 |
| J3xx | BG0-3IN to BG0-3Out and IACKIN to IACKOUT on slot 3 |
| J4xx | BG0-3IN to BG0-3Out and IACKIN to IACKOUT on slot 4 |
| J5xx | BG0-3IN to BG0-3Out and IACKIN to IACKOUT on slot 5 |
| J6xx | BG0-3IN to BG0-3Out and IACKIN to IACKOUT on slot 6 |
| J7xx | BG0-3IN to BG0-3Out and IACKIN to IACKOUT on slot 7 |
| J8xx | BG0-3IN to BG0-3Out and IACKIN to IACKOUT on slot 8 |
| J9xx | BG0-3IN to BG0-3Out and IACKIN to IACKOUT on slot 9 |
| J10xx | BG0-3IN to BG0-3Out and IACKIN to IACKOUT on slot 10 |
| J11xx | BG0-3IN to BG0-3Out and IACKIN to IACKOUT on slot 11 |
| J12xx | BG0-3IN to BG0-3Out and IACKIN to IACKOUT on slot 12 |
| J13xx | BG0-3IN to BG0-3Out and IACKIN to IACKOUT on slot 13 |
| J14xx | BG0-3IN to BG0-3Out and IACKIN to IACKOUT on slot 14 |
| J15xx | BG0-3IN to BG0-3Out and IACKIN to IACKOUT on slot 15 |
| J16xx | BG0-3IN to BG0-3Out and IACKIN to IACKOUT on slot 16 |
Backplane slots that share an adjacent P2 bus are marked with the same letter in the charts below.
| Slot | 1 | 2 | 3 |
|---|---|---|---|
| P2 Bus | A | A | A |
| Slot | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
|---|---|---|---|---|---|---|---|
| P2 Bus | A | B | B | C | D | A | A |
| Slot | 1 | 2 | 3 | 4 | 5 | 6 |
|---|---|---|---|---|---|---|
| P2 Bus | A | A | A | A | B | B |
| Slot | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| P2 Bus | A | A | A | A | A | A | B | C | D | E | E | E |
| Slot | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| P2 Bus | A | A | A | A | A | A | A | B | C | D | D | D |
| Slot | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| P2 Bus | A | A | A | A | A | A | A | B | C | D | E | E | F | F | F | G |