SAM47 INSTRUCTION SET
KS57C2308/P2308/C2316/P2316
5-50
DECS
— Decrement and Skip on Borrow
DECS
dst
Operation:
Operand
Operation Summary
Bytes
Cycles
R
Decrement register (R); skip on borrow
1
1 + S
RR
Decrement register pair (RR); skip on borrow
2
2 + S
Description:
The destination is decremented by one. An original value of 00H will underflow to 0FFH. If a
borrow occurs, a skip is executed. The carry flag value is unaffected.
Operand
Binary Code
Operation Notation
R
0
1
0
0
1
r2
r1
r0
R
←
R–1; skip on borrow
RR
1
1
0
1
1
1
0
0
RR
←
RR–1; skip on borrow
1
1
0
1
1
r2
r1
0
Examples:
1. Register pair HL contains the value 7FH (01111111B). The following instruction leaves the
value 7EH in register pair HL:
DECS HL
2. Register A contains the value 0H. The following instruction sequence leaves the value 0FFH
in register A. Since a "borrow" occurs, the “CALL PLAY1” instruction is skipped and the “CALL
PLAY2” instruction is executed:
DECS A
; "Borrow" occurs
CALL
PLAY1
; Skipped
CALL
PLAY2
; Executed
Summary of Contents for C2316
Page 30: ...ADDRESS SPACES KS57C2308 P2308 C2316 P2316 2 22 NOTES ...
Page 168: ...SAM47 INSTRUCTION SET KS57C2308 P2308 C2316 P2316 5 94 NOTES ...
Page 170: ......
Page 206: ...POWER DOWN KS57C2308 P2308 C2316 P2316 8 8 NOTES ...
Page 210: ...RESET KS57C2308 P2308 C2316 P2316 9 4 NOTES ...
Page 222: ...I O PORTS KS57C2308 P2308 C2316 P2316 10 12 NOTES ...
Page 272: ...LCD CONTROLLER DRIVER KS57C2308 P2308 C2316 P2316 12 24 NOTES ...
Page 280: ...SERIAL I O INTERFACE KS57C2308 P2308 C2316 P2316 13 8 NOTES ...
Page 294: ...MECHANICAL DATA KS57C2308 P2308 C2316 P2316 15 2 NOTES ...
Page 310: ...KS57P2308 P2316 OTP KS57C2308 P2308 C2316 P2316 16 16 NOTES ...
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