View source for Small Peripheral Controller

'''Small Peripheral Controller''' or '''SPC''' was [[DEC]]'s name for a board slot in the [[backplane]]s of [[UNIBUS]] [[PDP-11]]s into which small [[device controller]]s, etc, could be plugged. It was a [[DEC card form factor|quad]]-high slot, occupying [[DEC edge connector contact identification|rows C-F]] in a hex slot.

It was originally conceived to hold a dual-height device-specific card, along with single-height [[M105 Address Selector]] and [[M782 Interrupt Control]] [[FLIP CHIP]]s (later, the M7820 and M7821 revisions). (Among the dual-width controllers which did this were the [[KL11 asynchronous serial line interface‎|KL11]] (M780), the [[PC11 High-Speed Paper-Tape Reader/Punch Control|PC11]] (M781), the [[DR11-A parallel interface|DR11-A]] (M786), and the [[CR11 Controller|CR11]] (M829).)

The appropriate UNIBUS signal lines ([[address]], data, etc) were thus wired to the appropriate rows/pins in SPC slots. Other pins were wired to allow the necessary communication between the cards, without requiring cables between them.

It soon became more cost-effective to fabricate an entire device on a single quad card, but the pinout was retained. (For the pinout of an SPC slot, see [[UNIBUS#Pinout|here]].)

==Grants==

SPC slots were wired to bring all 5 UNIBUS [[bus grant line|grant lines]] through the device; this was performed in rows C (for [[Non-Processor Request and Grant|NPG]]) and D (for BGx).

The device board generally had a header which routed the grant (and matching request) line for the desired priority level to the [[interrupt]] [[circuit]]ry, and passed the other grant lines through. Un-occupied slots needed to have a [[G727 grant continuity card|G727]] installed.

The NPG grant line generally had a [[jumper]] on the backplane at each slot (between pins CA1 and CB1), which had to be removed if a [[DMA]] device was plugged into that slot, or installed if one was removed; alternatively, a [[G7273 grant continuity card]] could be installed.

==SPC Extensions==

On some systems, some SPC pins were recycled for other purposes.

In the [[PDP-11/04]] and [[PDP-11/34]], on the [[DD11-P backplane]] which holds the [[Central Processing Unit|CPU]] card(s), along with the [[KY11-LB Programmer's Console]] (which plugs into an otherwise-standard SPC slot), the CPU and the Programmer's Console do some communication via the backplane. Pins CP1 and CR1 are Halt Request and Halt Grant, respectively; they allow the KY11-B to tell the CPU to halt.

==Pinout==

The following table gives the pinout of an SPC slot. Pins are identified in the [[DEC edge connector contact identification|standard DEC manner]]. There are four connectors in a slot, C, D, E and F; pins on the component side are 1, those on the solder side are 2. Pins are identified by the '[[DEC alphabet]]', A-V, with G, I, O and Q dropped.

{| class="wikitable"
! Signal !! Assertion !! Termination !! Pin
|-
| colspan="4" style="text-align:center;" | Initialization and Shutdown
|-
| DC LO || L || Slow|| CN1
|-
| AC LO || L || Slow|| CV1
|-
| INIT || L || Fast || DL1
|-
| colspan="4" style="text-align:center;" | Arbitration
|-
| NPR || L || Fast || FJ1
|-
| BR7 || L || Fast || DD2
|-
| BR6 || L || Fast || DE2
|-
| BR5 || L || Fast || DF2
|-
| BR4 || L || Fast || DH2
|-
| NPG || H || Grant || In-CA1; Out-CB1
|-
| BG7 || H || Grant || In-DK2; Out-DL2
|-
| BG6 || H || Grant || In-DM2; Out-DN2
|-
| BG5 || H || Grant || In-DP2; Out-DR2
|-
| BG4 || H || Grant || In-DS2; Out-DT2
|-
| SACK || L || Fast || FT2
|-
| colspan="4" style="text-align:center;" | Addressing
|-
| A00 || L || Fast || EH2
|-
| A01 || L || Fast || EH1
|-
| A02 || L || Fast || EF1
|-
| A03 || L || Fast || EV2
|-
| A04 || L || Fast || EU2
|-
| A05 || L || Fast || EV1
|-
| A06 || L || Fast || EU1
|-
| A07 || L || Fast || EP2
|-
| A08 || L || Fast || EN2
|-
| A09 || L || Fast || ER1
|-
| A10 || L || Fast || EP1
|-
| A11 || L || Fast || EL1
|-
| A12 || L || Fast || EC1
|-
| A13 || L || Fast || EK2
|-
| A14 || L || Fast || EK1
|-
| A15 || L || Fast || ED2
|-
| A16 || L || Fast || EE2
|-
| A17 || L || Fast || ED1
|-
| colspan="4" style="text-align:center;" | Data
|-
| D00 || L || Fast || CS2
|-
| D01 || L || Fast || CR2
|-
| D02 || L || Fast || CU2, FE2%
|-
| D03 || L || Fast || CT2, FL1%
|-
| D04 || L || Fast || CN2, FN2%
|-
| D05 || L || Fast || CP2, FF1%
|-
| D06 || L || Fast || CV2, FF2%
|-
| D07 || L || Fast || CM2, FH1%
|-
| D08 || L || Fast || CL2, FK1%
|-
| D09 || L || Fast || CK2
|-
| D10 || L || Fast || CJ2
|-
| D11 || L || Fast || CH1
|-
| D12 || L || Fast || CH2
|-
| D13 || L || Fast || CF2
|-
| D14 || L || Fast || CE2
|-
| D15 || L || Fast || CD2
|-
| colspan="4" style="text-align:center;" | Control
|-
| C0 || L || Fast || EJ2
|-
| C1 || L || Fast || EF2
|-
| PA || L || Fast || CC1
|-
| PB || L || Fast || CS1
|-
| BBSY || L || Fast || FD1
|-
| MSYN || L || Fast || EE1
|-
| INTR || L || Fast || FM1
|-
| SSYN || L || Fast || EJ1, FC1%
|-
| colspan="4" style="text-align:center;" | Power
|-
| Ground || N/A || N/A || xC2
|-
| Ground || N/A || N/A || xT1
|-
| +5 || N/A || N/A || xA2
|-
| -15 || N/A || N/A || xB2
|}

Entries of the form 'xYN' mean that that is available on all 4 [[DEC edge connector contact identification|connectors]] (C, D, E and F) in each slot.

% For forward compatibility, use the first pin rather than the second.

==See also==

* [[Modified UNIBUS Device]]

[[Category: UNIBUS]]