
Preliminary Product Information
19
μ
PD78F9197Y
5.3
Processor Registers
5.3.1
Controller registers
(1) Program counter (PC)
The PC is a 16-bit register for holding address information that indicates the next program to be executed.
Figure 5-3. Program Counter Configuration
PC15
PC
PC14 PC13 PC12 PC11PC10 PC9 PC8 PC7 PC6 PC5 PC4 PC3 PC2 PC1 PC0
15
0
(2) Program status word (PSW)
The PSW is an 8-bit register for holding the status of the CPU according to the results of instruction execution.
Figure 5-4. Program Status Word Configuration
7
IE
0
Z
0
AC
0
0
1
CY
PSW
(a) Interrupt enable flag (IE)
IE is used to control whether interrupt requests are to be accepted by the CPU.
(b) Zero flag (Z)
Z is set (1) if the result of operation is zero. Otherwise, it is reset (0).
(c) Auxiliary carry flag (AC)
AC is set (1) if the result of the operation has a carry from bit 3 or a borrow to bit 3. Otherwise, it is reset (0).
(d) Carry flag (CY)
CY is used to indicate whether an overflow or underflow has occurred during the execution of a subtract or
add instruction.
(3) Stack pointer (SP)
SP is a 16-bit register for holding the start address of a stack area. The stack area can be specified only in an
area (FD00H to FEFFH) of internal high-speed RAM.
Figure 5-5. Stack Pointer Configuration
SP15
SP
SP14 SP13 SP12 SP11 SP10 SP9 SP8 SP7 SP6 SP5 SP4 SP3 SP2 SP1 SP0
15
0
Caution
A RESET input makes the SP content undefined. Before executing an instruction, always
initialize the SP.