GMS81508A Datasheet, PDF (15/91 Pages) Hynix Semiconductor – USERS MANUAL

HYUNDAI MicroElectronics
2.1.5. Program Counter
The program counter(PC) is a 16-bit counter which consists of 8-bit register PCH and PCL. The
addressing space is 64K bytes.
This counter indicates the address of the next instruction to be executed.
In reset state, the program counter (PC) has reset routine address in address FFFFH and FFFEH .
2.1.6. Program Status Word
PSW is an 8-bit register which is composed of flags to maintain the condition of the processor
immediately after an operation.
After RESET, The contents of PSW is set to "00H".
PSW
7
6
5
4
3
2
1
0
NVGBH
I
ZC

Carry Flag ( C )
After an operation, it is set to "1" when there is a carry from bit7 of ALU or not a borrow.
SETC,CLRC instructions allow direct access for setting and resetting.
it can be used as a 1-bit accumulator.
It is a branch condition flag of BCS, BCC instructions.
 Zero Flag ( Z )
After an operation including 16-bit operation, it is set to "1" when the result is “0”.
It is a branch condition flag of BEQ, BNE.

Interrupt Enable Flag ( I )
This flag is used to enable/disable all interrupts except interrupt caused by BRK instruction.
When this flag is "1", it means interrupt enable condition. When an interrupt is accept, this flag is
automatically set to "0" thereby preventing other interrupts. also it is set to "1" by RETI instruction.
This flag is set and cleared by EI, DI instructions.
 Half Carry Flag ( H )
After an operation, it is set when there is a carry from bit3 of ALU or is not a borrow from bit4 of
ALU.
It can not be set by any instruction. it is cleared by CLRV instruction like V flag.
10