Sh Ift C Ounte R; Program Counter; Accumulator; Multiplier Quotient - IBM 7090 Instruction-Reference

The "invert SI" has no effect on the SI position if there is no bit in the corresponding
position of the storage register. With a bit in the SR and the invert line active, the
information in the SI will be inverted.
7.1. 05 Shift Counter (Systems 03.04.14.1-03.04.19.1)
The shift counter is an 18-position counter of triggers. It is a step-down counter
when used for shifting. The shift counter is also used as part of the program register
for certain instructions. During a shifting operation, the counter will be stepped every
clock pulse (Figure 3.1-7A). Lines controlling the shift counter are:
AS to.SC
Step SC
02.11. 78.1
02.11. 79.1
7.1.06 Program Counter (Systems 03. 05. 00. 1-03. 05. 07. 1)
The program counter is a 16-position counter of triggers. These positions are
labeled 2 through 17 (Figure 3. 1-7B). Lines controlling the program counter are:
ADV PROG CTR
PC to AS
02.11. 51.1
03.05.09.1
The program counter is a count-up counter, and can sequentially step through a
program.
7.1. 07 Accumulator (Systems 02.03.00.1-02.03.37.1)
The accumulator is a 38-position register of shift cells. Some trouble may result
from the "CP set" being in error. This is true for all registers made up of shift cells.
Do not vary the "CP set" until all other possibilities have been checked. Refer to
Section 7 for adjustment of the "CP set." Lines controlling the accumulator are shown
in Figure 7 . 1-5.
Shift Right 02.12.36.1
Shift Left 02.12.35.1
SR to ACC 02.10.15.1
Adder to AC
02.12.32.1
Set ACC 02.05.03.1
Hold ACC 02.05.03.1
7.1. 08 Multiplier Quotient (Systems 02.04.00.1-02.04.35.1)
The MQ is a 36-position register of shift cells. The MQ is used on multiply and
divide operations, although some other operations may use it (Figure 7. 1-4). Lines
that control the MQ are:
SR to MQ
Shift MQ Left
Shift MQ Right
Set MQ
Hold MQ
02.12.40.1
02.12.44.1
02.12.45.1
J
02.05.04 and
102.05.05.1
168