NSC800 Datasheet, PDF (56/76 Pages) National Semiconductor (TI) – NSC800TM High-Performance Low-Power CMOS Microprocessor

12 14 Program Control (Continued)
DJNZ d
Decrement the B register and conditionally jump to program
location calculated with respect to the program counter and
the displacement d based on the contents of the B register
BwBb1
No flags affected
If B e 0 continue
w else PC PC a d
76543210
00010000
db2
Timing If B ⁱ 0
If B e 0
Addressing Mode
M cycles 3
T states 13 (5 3 5)
M cycles 2
T states 8 (5 3)
PC Relative
CALLS
CALL nn
Unconditional call to subroutine at location nn
w (SP b 1)
PC_H
w (SP b 2)
PC_L
SP w SP b 2
No flags affected
PC w nn
76543210
11001101
n (low-order byte)
n (high-order byte)
Timing
Addressing Mode
M Cycles
T states
Direct
5
17 (4 3 4 3 3)
CALL cc nn
Conditional call to subroutine at location nn based on test-
able flag stages
If cc true
No flags affected
w (SP b 1)
PC_H
w (SP b 2)
PC_L
SP w SP b 2
PC w nn
else continue
765 4 3210
11
cc
100
RETURNS
RET
Unconditional return from subroutine or other return to pro-
gram location pointed to by the top of the stack
w PC_L
(SP)
No flags affected
w PC_H
(SP a 1)
SP w SP a 2
76543210
11001001
Timing
M cycles 3
T states 10 (4 3 3)
Addressing Mode
Register Indirect
RET cc
Conditional return from subroutine or other return to pro-
gram location pointed to by the top of the stack
If cc true
No flags affected
w PC_L
(SP)
w PC_H
(SP a 1)
SP w SP a 2
else continue
76543210
1 1 cc 0 0 0
Timing If cc true
If cc not true
Addressing Mode
M cycles 3
T states 11 (5 3 3)
M cycles 1
T states 5
Register Indirect
RETI
Unconditional return from interrupt handling subroutine
Functionally identical to RET instruction Unique opcode al-
lows monitoring by external hardware
w PC_L
(SP)
No flags affected
w PC_H
(SP a 1)
SP w SP a 2
76543210
11101101
01001101
Timing
Addressing Mode
M cycles 4
T states 14 (4 4 3 3)
Register Indirect
n (low-order byte)
n (high-order byte)
Timing If cc true
If cc not true
Addressing Mode
M cycles 5
T states 17 (4 3 4 3 3)
M cycles 3
T states 10 (4 3 3)
Direct
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