PDP-11/05

PDP-11/05
a PDP11/05 from a sales brochure.
Manufacturer:	Digital Equipment Corporation
Architecture:	PDP-11
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 KA11-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 KA11-B was a two-board micro-programmed processor contained on two hex cards.

The PDP-11/05 was identical to the PDP-11/10; the only difference between the PDP-11/05 and the PDP-11/10 was the number on the front panel. The PDP-11/05 was aimed toward the OEM market, while the PDP-11/10 was intended for end-users.

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.

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