RCA 301, Programmer'S Reference Manual

Page: 81 / 235

Y C ompare Left (COM)
General Description
This instruction is used to determine the relative magnitude of two operands of equal length. The resulting PR1
settings permit alternate sequence of action.
Format
Operation —Y
N — Number (0-44) characters to be compared. (See Appendix F-I.)
A Address — HSM address of leftmost character of first operand.
B Address — HSM address of leftmost character of second operand.
Direction of Operation
Left to right.
Outline of Operation
This instruction initially sets PRZ and operates in the following cycles:
The contents of the N Register are examined. If zero, the instruction terminates. If other than zero, the contents
of the HSM locations specified by the A and B Registers are transferred to the D
2
and D
:!
positions of the D
Register respectively. The contents of the A and B Registers are incremented by one. The contents of D
2
and D
:
are compared. If the contents of D
2
are greater than the contents of D
(
, PRP is set, and the instruction terminates.
If the contents of D, are greater than the contents of D
2
, PRN is set, and the instruction terminates. If the contents
of D. equal the contents of D„ the contents of the N Register are decremented by one, and the cycle is repeated.
Final Register Contents
(A)
t
= Address of location one to the right of the last character compared in first operand.
(B)
r
= Address of location one to the right of the last character compared in second operand.
PRI
PRI set according to outline of operation. ' ! v\ \ t > a i
CK, V 1® \ "R*.
I
^
>
Timing
Total time in microseconds
= 2In + 35, where n equals the number of characters compared.
Example #1
Instruction:
Operation N A Address B Address
Y 5 1001 1007
HSM before and after Instruction is Executed:
1001 1002 1003
1004 1005 1006
1007 1008 1009
1010 1011
1012
s
M I
T H
—
s
M I
T
H
—
VII-7