NEC PD750008 - Manual (Page 82)

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µPD750008 USER'S MANUAL
4.8 PROGRAM STATUS WORD (PSW): 8 BITS
The program status word (PSW) consists of various flags closely associated with processor operations.
The PSW is mapped to addresses FB0H and FB1H in data memory space. Four bits at address FB0H
can be manipulated with a memory manipulation instruction.
Figure 4-16. Program Status Word Format
Table 4-3. PSW Flags Saved/Restored in Stack Operation
Saved/restored flag
Save When a CALL, CALLA, or CALLF instruction is executed MBE and RBE are saved.
When a hardware interrupt occurs All PSW bits are saved.
Restore When a RET or RETS instruction is executed MBE and RBE are restored.
When a RETI is executed All PSW bits are restored.
(1) Carry flag (CY)
The carry flag is a 1-bit flag used to store information about an overflow or underflow that occurs when
an arithmetic operation with a carry (ADDC, SUBC) is executed.
The carry flag functions as a bit accumulator, and therefore can be used to store the result of a Boolean
algebra operation performed on the CY and a bit at a specified data memory bit address.
The carry flag is manipulated using special instructions, independently of the other PSW bits.
A RESET signal causes the carry flag to be undefined.
RBE MBE IST0 IST1 SK0 SK1 SK2 CY
Address
Can be manipulated
by an instruction
specifically provided
for controlling this flag
Cannot be manipulated Can be manipulated
Symbol
PSW
FB1H FB0H
FB0H