ADDRESS SPACES KS57C2308/P2308/C2316/P2316
2-16
PROGRAM COUNTER (PC)A 13-bit program counter (PC) stores addresses for instruction fetches during program execution (KS57C2316
microcontroller has 14-bit program counter, PC0–PC13). Whenever a reset operation or an interrupt occurs, bits
PC12 through PC0 (PC13 through PC0 for KS57C2316) are set to the vector address.
Usually, the PC is incremented by the number of bytes of the instruction being fetched. One exception is the
1-byte REF instruction which is used to reference instructions stored in the ROM.
PROGRAM STATUS WORD (PSW)The program status word (PSW) is an 8-bit word that defines system status and program execution status and
which permits an interrupted process to resume operation after an interrupt request has been serviced. PSW
values are mapped as follows:
(MSB) (LSB)
FB0H IS1 IS0 EMB ERB
FB1H CSC2 SC1 SC0
The PSW can be manipulated by 1-bit or 4-bit read/write and by 8-bit read instructions, depending on the specific
bit or bits being addressed. The PSW can be addressed during program execution regardless of the current value
of the enable memory bank (EMB) flag.
Part or all of the PSW is saved to stack prior to execution of a subroutine call or hardware interrupt. After the
interrupt has been processed, the PSW values are popped from the stack back to the PSW address.
When a RESET is generated, the EMB and ERB values are set according to the RESET vector address, and the
carry flag is left undefined (or the current value is retained). PSW bits IS0, IS1, SC0, SC1, and SC2 are all
cleared to logical zero.
Table 2-5. Program Status Word Bit Descriptions
PSW Bit Identifier Description Bit Addressing Read/Write
IS1, IS0 Interrupt status flags 1, 4 R/W
EMB Enable memory bank flag 1R/W
ERB Enable register bank flag 1R/W
CCarry flag 1R/W
SC2, SC1, SC0 Program skip flags 8R