Shift Instructions: RTE (Rotate Right Accumulator and Extension)

Rotate Right Accumulator and Extension
Organizational graphic tag to help group instructions

Mnemonic

RTE

Description

The basic purpose of this instruction -- indicated by the term rotate -- is to take the bits shifted out of accumulator-extension position 15 and shift them back into accumulator-position 0 (no bits are lost).

Rotate Right Accumulator and Extension example 1, showing two shifts with emphasis on bit preservation

The number of positions shifted is specified by a shift count. Location of the shift count is determined by the T bits in the instruction:

T Bits (6 and 7)		Shift Count Location
00		Low-order six bits of displacement (in the shift instruction)
01		Low-order six bits in index-register 1
10		Low-order six bits in index-register 2
11		Low-order six bits in index-register 3

A value must be put into the shift-count location before the operation is started. The operation is ended when the specified number of shifts have been performed. The shift count, however, need be set up only once. After the operation is ended, the original shift count is the same as its initial value. (Decrementing of the count is performed in separate circuits.)

Maximum shift count that can be specified is 63 (111111 in binary). A count of 31 shifts the value of accumulator-position 0 to extension-position 15; a count of 16 (or 48) reverses the positions of the two words -- the one in the accumulator and the one in the accumulator extension:

Rotate Right Accumulator and Extension example 2: showing the swapping of the A and Q registers

A shift count of zero (000000 in binary) causes this instruction to perform as a no-operation: contents of the accumulator and extension remain unchanged.

Core storage is not addressed during execution of the rotate-right-accumulator-and-extension instruction.

Indicators: The carry and overflow indicators are not affected during execution of the RTE instruction.

Examples

Shift Left Accumulator and Extension

Assembler Language Coding Hexadecimal Value Description of Instruction

Label Operation F T

21 25

27 30

32

33

35..40..

RTE DISP 18*X Contents of A and Q rotate right the number of counts in DISP

RTE 1 19C0 Contents of A and Q rotate right the number of counts in XR1

RTE 2 1AC0 Contents of A and Q rotate right the number of counts in XR2

RTE 3 1BC0 Contents of A and Q rotate right the number of counts in XR3

* This hexadecimal digit can be C, D, E, or F depending upon the desired shift count.

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