Processor Registers; Control Registers - NEC 78K0S/KU1+ User Manual

3.2 Processor Registers

The 78K0S/KU1+ provide the following on-chip processor registers.

3.2.1 Control registers

The control registers have special functions to control the program sequence statuses and stack memory. The
control registers include a program counter, a program status word, and a stack pointer.
(1) Program counter (PC)
The program counter is a 16-bit register which holds the address information of the next program to be
executed.
In normal operation, the PC is automatically incremented according to the number of bytes of the instruction to
be fetched. When a branch instruction is executed, immediate data or register contents are set.
Reset signal generation sets the reset vector table values at addresses 0000H and 0001H to the program
counter.
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PC PC15 PC14 PC13 PC12 PC11 PC10 PC9
(2) Program status word (PSW)
The program status word is an 8-bit register consisting of various flags to be set/reset by instruction execution.
Program status word contents are stored in stack area upon interrupt request generation or PUSH PSW
instruction execution and are restored upon execution of the RETI and POP PSW instructions.
Reset signal generation sets PSW to 02H.
PSW
CHAPTER 3 CPU ARCHITECTURE
Figure 3-7. Program Counter Configuration
PC8
Figure 3-8. Program Status Word Configuration
7
IE Z 0 AC
User's Manual U18172EJ2V0UD
PC7 PC6 PC5 PC4 PC3
0
0 0 1 CY
0
PC2 PC1 PC0
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