UPD6P8 NEC [NEC], UPD6P8 Datasheet - Page 14

• Manufacturer Part Number: UPD6P8
• Description: MOS INTEGRATED CIRCUIT 4-BIT SINGLE-CHIP MICROCONTROLLER FOR INFRARED REMOTE CONTROL TRANSMISSION
• Manufacturer: NEC [NEC]

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3. INTERNAL CPU FUNCTIONS
3.1 Program Counter (PC): 11 Bits
are automatically incremented in accordance with the instruction length (byte count) each time an instruction is
executed.
address written in the operand.
entered in the PC after the PC contents at the time are saved in the address stack register (ASR). If the return
instruction (RET) is executed after the CALL instruction is executed, the address saved in the ASR is restored to
the PC.
3.2 Stack Pointer (SP): 1 Bit
the return instruction (RET) is executed.
reset signal is generated, and the PC becomes 000H.
by means of a program.
3.3 Address Stack Register (ASR (RF)): 11 Bits
ASR value even after the RET instruction is executed.
The program counter (PC) is a binary counter that holds the address information of the program memory.
The PC contains the address of the instruction that should be executed next. Normally, the counter contents
However, when executing jump instructions (JMP, JC, JNC, JF, JNF), the PC contains the jump destination
When executing the subroutine call instruction (CALL), the call destination address written in the operand is
After reset, the value of the PC becomes “000H”.
This is a 1-bit register that holds the status of the address stack register.
The stack pointer contents are incremented when the call instruction (CALL) is executed and decremented when
When reset, the stack pointer contents are cleared to 0.
When the stack pointer overflows (stack level 2 or more) or underflows, the CPU is defined as hung up, a system
As no instruction is available to set a value directly for the stack pointer, it is not possible to operate the pointer
The address stack register saves the return address of the program after a subroutine call instruction is executed.
The lower 8 bits are allocated in RF of the data memory as a alternate-function RAM. The register holds the
After reset, it holds the previous data (undefined when turning on the power).
Caution If RF is accessed as the data memory, the higher 4 bits become undefined.
ASR
PC
ASR10
PC10
PC9
ASR9
Figure 3-2. Address Stack Register Configuration
PC8
Figure 3-1. Program Counter Configuration
ASR8
PC7
Data Sheet U17848EJ3V0DS
ASR7
PC6
ASR6
PC5
ASR5
PC4
ASR4
PC3
RF
PC2
ASR3
PC1
ASR2
PD6P8, 6P8A, 6P8B
PC0
ASR1
ASR0