KE11-A Extended Arithmetic Element
The KE11-A Extended Arithmetic Element is an autonomous UNIBUS peripheral which can perform a variety of arithmetic or logical operations:
- multiplication
- division
- multi-bit shifts
- logical shift
- arithmetic shift
- normalization
(The last is used for implementation of floating point in software.)
It is implemented as several quad and dual boards, plugged into a custom four-slot system unit (details below).
The KE11-A was originally produced for use with the PDP-11/20, whose KA11 CPU did not have multiply, divide, or multi-bit shift operations. As a UNIBUS peripheral, not integrated into the CPU, it was also usable with other models, e.g. the PDP-11/05 and PDP-11/04, which likewise did not implement multiplication in hardware, etc.
The KE11-A can be operated with an optional KM11-A Maintenance Set in order to diagnose faults.
It was replaced by the KE11-B Extended Arithmetic Element, a program compatible re-implementation on a single hex card.
Registers
The device has a number of registers, which can be configured to sequential locations in the I/O page; most are words, but there are two byte registers. It is normally configured to addresses 777300-777316; a second KE11-A, if present, is configured to addresses 777320-777336. The operation to be performed is selected by the register which data is written to. Registers which hold results are readable, but many of the operation selection registers are write-only. In the register table (below), those which are read/write are shown in normal font; those which are read-only are in italics; those which are write-only in bold (these return '0' when read).
| Register | Abbreviation | Address | Size |
|---|---|---|---|
| Multiply | MUL | 777310 | W |
| Accumulator | AC | 777302 | W |
| Multiplier-Quotient | MQ | 777304 | W |
| Divide | DIV | 777306 | W |
| Step Counter$ | SC | 777310 | B |
| Status Register% | SR | 777311 | B |
| Normalize | NOR | 777312 | W |
| Logical Shift | LSH | 777314 | W |
| Arithmetic Shift | ASH | 777316 | W |
$ The SC is read-only as an individual byte, but can written as a word together with the SR.
% The SR is read-only as an individual byte, but can written as a word together with the SC.
Division takes as one operand a 32-bit value held in the AC (high order) and MQ (low order); a remainder is left in the AC. Multiplication produces a 32-bit product in the AC (high order) and MQ (low order). Both arithmetic and logical shifts operate on a 32-bit value held in the AC (high order) and MQ (low order).
Status Register (SR)
| Overflow XOR Negative | Negative | AC = -1 | AC = 0 | MQ = 0 | AC = MQ = 0 | AC = MQ15 | Carry |
| 07 | 06 | 05 | 04 | 03 | 02 | 01 | 00 |
Hardware
The KE11-A consists of 3 quad boards:
- M7210 Data Control
- M7211 Register Control
- M827 Clock and States
and a pair of M234 Register dual-height boards, plugged into the quad custom backplane.
Board locations
These are the board locations for the KE11-A (as seen from the board side of the backplane):
| Connector | ||||||
|---|---|---|---|---|---|---|
| Slot | A | B | C | D | E | F |
| 1 | UNIBUS In | M7210 Data Control | ||||
| 2 | Unused | KM11-A | M234 Register (low byte) |
M234 Register (high byte) | ||
| 3 | G772 Power |
Reserved | M7211 Register Control | |||
| 4 | UNIBUS Out | M827 Clock & States | ||||
