D6600A NEC, D6600A Datasheet - Page 4

• Manufacturer Part Number: D6600A
• Description: Search -----> UPD6600A
• Manufacturer: NEC

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4
1.
according to the number of instruction bytes.
Then, a value needed for each jump instruction will be loaded.
into the PC.
2.
memory.
return instruction (RET) is executed.
data memory as the stack area.
will be generated.
The program counter (PC) is a binary counter, which holds the address information for the program memory.
Normally, the program counter contents are automatically incremented each time an instruction is executed,
When executing a jump instruction (JMP0, JC, JF), the program counter indicates the jump destination.
Immediate data or the data memory contents are loaded to all or some bits of the PC.
When executing the call instruction (CALL0), the PC contents are incremented (+1) and saved into the stack memory.
When executing the return instruction (RET), the stack memory contents are double incremented (+2) and loaded
When “all clear” is input or on reset, the PC contents are cleared to “000H”.
This 2-bit register holds the start address information for the stack area. The stack area is shared with the data
The SP contents are incremented, when the call instruction (CALL0) is executed. They are decremented, when the
The stack pointer is cleared to “00B” after reset or “all clear” is input, and indicates the highest address FH for the
The figure below shows the relationship for the stack pointer and the data memory area.
If the stack pointer overflows or underflows, it is determined that the CPU overflows, and the PC internal reset signal
PROGRAM COUNTER (PC) ……… 9 BITS
STACK POINTER (SP) ……… 2 BITS
PC
9
PC
PC
Figure 1-1. Program Counter Organization
8
8
PC
PC
7
7
PC
PC
Data memory
6
6
10 BITS
PC
PC
(a)
(b)
5
5
PC
PC
PD6600A
:
:
PD6124A
4
4
PD6600A
PD6124A
PC
PC
3
3
R
R
R
R
PC
PC
C
D
E
F
2
2
(SP)
PC
PC
11B
10B
01B
00B
1
1
PC
PC
0
0
PC
PC
PD6124A, 6600A