PDP-11/05

A PDP-11/05 from a sales brochure.

PDP-11/05
Manufacturer:	Digital Equipment Corporation
Architecture:	PDP-11
Year Introduced:	June 1972
Word Size:	16 bit
Physical Address Size:	18 bit (only 16 bits usable)
Bus Architecture:	UNIBUS

The PDP-11/05 was the fourth processor in the PDP-11 series, following the PDP-11/20, the PDP-11/45 and the PDP-11/40; it used the KD11-B CPU. It was intended as a cost-reduced low-end machine to replace the PDP-11/20. Like all the other early PDP-11's, it was a UNIBUS machine.

The PDP-11/05 was identical to the PDP-11/10; the only difference between the /05 and the /10 was the number on the front panel. The /05 was aimed toward the OEM market, while the /10 was intended for end-users. General usage (following DEC's lead) is to refer to all these machines as '11/05s'.

The KD11-B was a two-board micro-programmed processor contained on two hex cards.

Backplane versions

The PDP-11/05 and /10 came in three versions, with different main backplanes (the 9-slot unit holding the two CPU cards).

The original /05 and /10 came with backplanes wired to hold MM11-L 16 Kbyte core memory units. There were two different backplanes: one held two memory units, with one slot left for SPC devices; the other held one memory unit, and provided four SPC slots.

A second version, the /05N and /10N, came in a 10-1/2 inch box and had a slightly different backplane, which had space for two MM11-L memory units, but deleted the SPC slot of the previous double MM11-L backplane, and replaced it with a slot to hold the dual-height M9970 console terminal cable board.

The later /05S and /10S came with a backplane wired to hold an MM11-U 32 Kbyte core memory, and which provided three SPC slots.

CPU board versions

The two boards in the PDP-11/05-10 (the M7260 data paths module, and the M7261 control logic module) both come in two markedly-different versions, but unlike later practise (as in, e.g. the PDP-11/34), the two versions are not given different M-numbers, or clearly marked with a revision (i.e. 'M7260' and 'M7260-AA') on the handles.

One easy way to visually distinguish the early M7260 from later ones is that the later ones contain a circular selector switch in the upper left corner to select the baud rate of the built-in serial line; also, the position of the large UART chip has a different location (from down near the contact fingers, to up near the handles) and orientation (parellel to the board's long axis, in the earlier revision). For the M7261, the early version of the board has a large blank area, containing only traces, in the left middle area of the board.

The early revision of the M7260 is the 'B' revision; the later is the 'C' revision (the latter is marked as such, on the back side of the board- "M7260C"). For the M7261, two early revisions are the 'C' and 'E' revisions (the latter also similarly marked - "M7261E"); the later is the 'F' (also marked).

The early version of the M7260 only supports 110 baud operation; the latter has a circular selector switch which allows operation at a range of speeds from 110 baud up to 2400 baud; however, it is necessary to tweak a trim pot to change from the 110/220/440/880/1760 speed set to the 150/300/600/1200/2400 set.

The later revision of the M7261 contains two jumpers which are not present on the earlier revision. One (W1) disables to built-in serial line (which is 20mA, and limited to 2400 baud), allowing use of a more capable serial interface as the system console. The other (W2) disables the CPU from acting as a bus arbitrator, so that the machine can be a 'slave' processor, on a UNIBUS controlled by another CPU.

Control PROMs

The KD11-B makes extensive use of PROMs in place of random logic for control purposes; both boards contain a large number of PROMs. The two types used are IM5600 (or equivalent) 32x8 PROM, the IM5603 256x4 PROM (on the M7261), and the 74187 256x4 PROM (on the M7260).

On the early version (etch revision B) of the M7260 Data Paths board:

Part Number	Package	Type
A01A1	E25	32x8
A02A1	E53	32x8
A03A1	E61	32x8
A03A2	E59	256x4
A04A1	E64	32x8
A05A1	E66	32x8
A06A1	E68	32x8
A08A1	E69	32x8
A10A1	E71	32x8
A11A1	E74	32x8
A12A1	E82	32x8

On the later version (etch revision C) of the M7260 Data Paths board (apparently all the same parts, but mostly in different locations; differing locations are marked with a '*'):

Part Number	Package	Type
A01A1	E44*	32x8
A02A1	E53	32x8
A03A1	E54*	32x8
A03A2	E72*	256x4
A04A1	E65*	32x8
A05A1	E59*	32x8
A06A1	E66*	32x8
A08A1	E78*	32x8
A10A1	E77*	32x8
A11A1	E83*	32x8
A12A1	E69*	32x8

The following table provides information on the PROMs on the early version (C and E etch revisions) and late version (F etch revision) of the M7261 Control Logic and Microprogram board:

Function	Type	Part #	Rev. C	Rev. E	Rev. F
Bus Request -> Grant processing	256x4	A01A2	E12		E24
Internal address decode (first stage)	256x4	A02A2	E30		E53
Microprogram - Next instruction (high bits)	256x4	A04A2	E92		E102
Microprogram - Processor Status Word control	256x4	A05A2	E93		E104
Internal address decode (second stage)	32x8	A07A1	E68		E71
Microprogram - Bus control	256x4	A07A2	E95
		A17A2		E95	E106
Internal address decode (second stage)	32x8	A09A1	E69		E72
Branch utest service	256x4	A09A2	E101		E107
Microprogram - Next instruction (low bits)	256x4	A10A2	E103		E112
Microprogram - ALU operation select	256x4	A11A2	E104		E114
Microprogram - Branch utest	256x4	A12A2	E105
		A18A2			E113
Internal interrupt acknowledge	32x8	A13A1	E90
Microprogram - Multiplexor control	256x4	A13A2	E106		E115
Console switch control	32x8	A14A1	E100		E108
		A16A1		E100
Microprogram - Bus control	256x4	A14A2	E107
		A19A2			E116
Microprogram - ALU control	256x4	A15A2	E94
		A20A2			E103
Microprogram - Miscellaneous	256x4	A16A2	E96		E105

On the later version (F etch revision) of the M7261 Control Logic and Microprogram board, the parts are mostly the same parts as the previous revision, but the chip numbering system for the board has been completely revised.

Note that the 'F' etch revision has one less PROM than the 'E' revision, but it is not a micro-program PROM - the 'missing' chip is a 32x8 PROM used for internal interrupt functions; it was replaced by a 74154 4->16 demultiplexor (E110).

It appears that on an earlier revision of the prints, the chip in E96 (A16A2 in the C etch revision) was actually a different version, A8A2; the prints for the C etch revision show the later one in the parts list, but the earlier one in the actual drawing.

For the E etch revision, the actual drawing shows an A14A1 at location E100, not an A16A1, but the later one is in the parts list.

Prints

Prints for both major versions of the CPU cards are available online; the earlier ones may be found in the GT40 Engineering Drawings set dated February, 1973 (pp. 141-150 for the M7260, and pp. 162-173 for the M7261).

The following table contains details of exactly which board etch revisions are covered in which sets of prints, for both boards:

Drawing Set	Date	M7260	M7261
PDP-11/05 Engineering Drawings, Revision B (not online yet)	May, 1972	B	C
GT40 Engineering Drawings	February, 1973	B	E
PDP-11/05S System Engineering Drawings, Revision D	October, 1974	C	F
PDP-11/05 Engineering Drawings, Revision AH	July, 1976	C	F

Keys

Unlike all the other PDP-11s, which use a circular Ace key, the /05's (and /10s) use a normal flat Yale-type key. The original key is a Chicago Lock Company key, code "GRB 2"; this is cut 215, on a Chicago K5K or Ilco S1041T blank. If simply duplicating an existing key, Hillman Y11 and FR4 blanks may be used (both work, but one has to be trimmed a bit, length-wise).

Gallery