SN8P2604A
8-Bit Micro-Controller
2.1.4.5 PROGRAM COUNTER
The program counter (PC) is a 12-bit binary counter separated into the high-byte 4 and the low-byte 8 bits. This
counter is responsible for pointing a location in order to fetch an instruction for kernel circuit. Normally, the program
counter is automatically incremented with each instruction during program execution.
Besides, it can be replaced with specific address by executing CALL or JMP instruction. When JMP or CALL instruction
is executed, the destination address will be inserted to bit 0 ~ bit 11.
Bit 15 Bit 14 Bit 13 Bit 12 Bit 11 Bit 10 Bit 9 Bit 8 Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
PC
-
-
-
-
PC11 PC10 PC9 PC8 PC7 PC6 PC5 PC4 PC3 PC2 PC1 PC0
After
reset
-
-
-
-
0
0
0
0
0
0
0
0
0
0
0
0
PCH
PCL
)
ONE ADDRESS SKIPPING
There are nine instructions (CMPRS, INCS, INCMS, DECS, DECMS, BTS0, BTS1, B0BTS0, B0BTS1) with one
address skipping function. If the result of these instructions is true, the PC will add 2 steps to skip next instruction.
If the condition of bit test instruction is true, the PC will add 2 steps to skip next instruction.
B0BTS1
JMP
…
FC
C0STEP
; To skip, if Carry_flag = 1
; Else jump to C0STEP.
…
C0STEP:
NOP
B0MOV
B0BTS0
JMP
A, BUF0
FZ
C1STEP
; Move BUF0 value to ACC.
; To skip, if Zero flag = 0.
; Else jump to C1STEP.
…
…
C1STEP:
NOP
If the ACC is equal to the immediate data or memory, the PC will add 2 steps to skip next instruction.
CMPRS
JMP
…
A, #12H
C0STEP
; To skip, if ACC = 12H.
; Else jump to C0STEP.
…
C0STEP:
NOP
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