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3.5
STEP 5 Operations with Examples
Accumulators as working
registers
ACCU 1
High byte
1)
31
ACCU-1-HH
ACCU-1-H
1)
analogous for ACCU 2 to ACCU 4
CPU 948 Programming Guide
C79000-G8576-C848-04
A STEP 5 operation consists of the operation and an operand. The
operation specifies what the CPU is to do (operation). The operand
specifies with what an operation is to be executed.
STEP 5 operations can be divided into the following groups:
• • basic operations (can be used in all logic blocks),
• • supplementary operations,
• • executive operations (can only be used in FB/FX function blocks),
• • semaphore operations (can only be used in FB/FX function blocks).
The CPU 948 has four accumulators, ACCU 1 to ACCU 4. Most
STEP 5 operations use two 32-bit registers (ACCU 1 and ACCU 2) as
the source of operands and the destination for results.
High word
Low byte
24 23
16 15
ACCU-1-HL
The STEP 5 operation to be carried out affects the accumulators, e.g.:
• • ACCU 1 is always the destination in load operations. A load
operation shifts the old contents of ACCU 1 to ACCU 2 (stack
lift). Accumulators 3 and 4 are not changed by any load operations.
STEP 5 Operations with Examples
Low word
High byte
Low byte
8 7
ACCU-1-LH
ACCU-1-LL
ACCU-1-L
0
3 - 15
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