Computer Hardware User's Guide

RPTB Repeat Block
13-210
Example RPTB 127h
Before Instruction After Instruction
PC 0123 PC 0124
RE 0 RE 127
RS 0 RS 124
ST 0 ST 100
LUF 0 LUF 0
LV 0 LV 0
UF 0 UF 0
N 0 N 0
Z 0 Z 0
V 0 V 0
C 0 C 0
Because the block-repeat modes modify the program counter, no
other instruction can modify the program counter at the same time.
The following two rules apply:
Rule 1: The last instruction in the block (or the only instruction in a
block of size 1) cannot be a B cond , BR, DB cond , CALL,
CALL
cond , TRAP cond , RETI cond , RETS cond , IDLE, IDLE2,
RPTB, or RPTS. Example 7–3 on page 7-6 shows an
incorrectly placed standard branch.
Rule 2: None of the last four instructions at the bottom of the block
(or the only instruction in a block of size 1) can be a
B cond D, BRD, or DB cond D. Example 7–4 on page 7-7
shows an incorrectly placed delayed branch.
If either rule is violated, the PC will be undefined.