CHAPTER 3 CPU ARCHITECTURE
User’s Manual U18172EJ2V0UD
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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.
Figure 3-7. Program Counter Configuration
0
15
PC14
PC15
PC
PC13 PC12 PC11 PC10
PC9
PC8
PC7
PC6
PC5
PC4
PC3
PC2
PC1
PC0
(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.
Figure 3-8. Program Status Word Configuration
7
0
IE
Z
0
AC
0
0
1
CY
PSW