KE11-A Extended Arithmetic Element

The KE11-A Extended Arithmetic Element is an Extended Arithmetic Element implemented as autonomous UNIBUS peripheral; it 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 backplane (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 (plugged into slot B02) 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
Divide	DIV	777300	W
Accumulator	AC	777302	W
Multiplier-Quotient	MQ	777304	W
Multiply	MUL	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

See also

• KE11-B Extended Arithmetic Element

Further reading

• KE11-A User's Guide (EK-KE11A-OP ?)

External links

• pdp11/20-15-r20 processor handbook - the operation of the KE11-A is covered in Chapter 8 (pp. 155-162 of the PDF)
• KE11-A extended arithmetic element (DEC-11-HKEA-D)
• KE11-A extended arithmetic element engineering drawings