NEC PD75402A - Manual (Page 50)

CHAPTER 4. INTERNAL CPU FUNCTIONS
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4.7 PROGRAM STATUS WORD (PSW) ..... 8 BITS
The program status word (PSW) consists of various flags concerning closely the processor operation. Fig. 4-10
shows its configuration.
Saved to the stack memory per 8 bits at the interrupt acceptance and restored from the stack memory per 8 bits
at the RETI instruction execution (see Figs. 4-8 and 4-9).
Fig. 4-10 Program Status Word Configuration
The PSW is not assigned to the data memory space. So it is impossible to operate each flag by the memory
manipulation instruction. The carry flag (CY) alone is operable by a dedicated instruction, however.
IST0 turns 0 and SK0 to SK2 and CY turn indeterminate at RESET input.
(1) Carry flag (CY)
The carry flag is a 1-bit flag to store the overflow occurrence information at the operation instruction with carry
(ADDC) execution.
The carry flag also has the function of the bit accumulator, so it can perform Boolean operation with the bit address
specify data memory and can store its results.
The carry flag is operated by a dedicated instruction irrespective of the other PSW bits.
The carry flag turns indeterminate with the RESET input.
Table 4-1 Carry Flag Manipulation Instructions
Instruction (Mnemonic) Carry Flag Operation, Process
SET1 CY
CLR1 CY
NOT1 CY
SKT CY
AND1 CY, fmem.bit
OR1 CY, fmem.bit
XOR1 CY, fmem.bit
At interrupt execution
RETI
Set (1) CY
Clear (0) CY
Invert the content of CY
Skip if the content of CY is 1
Take AND/OR/XOR of the contents bit of the specified bit and CY
and store the result in CY
Save to the stack memory in 8 bits parallel to the other PSW bits
Restore from the stack memory in parallel to the other PSW
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Skip Flag
Interrupt Status Flag
Carry Flag
7 6 5 4 3 2 1 0
CY SK2 SK1 SK0 0 IST0 0 0
Interrupting process
Bit Boolean instruction
Carry flag manipulation
dedicated