UPD75238GJ

Manufacturer Part NumberUPD75238GJ
Description4 BIT SINGLE-CHIP MICROCOMPUTER
ManufacturerNEC [NEC]
UPD75238GJ datasheet
 
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Page 36/190

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(1) Carry flag (CY)
The carry flag is a 1-bit flag used to store overflow or underflow occurrence information when an arithmetic
operation with a carry (ADDC, SUBC) is executed.
The carry flag also has the function of a bit accumulator, and therefore can be used to store the result of
a Boolean operation performed on the CY and 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 occurrence causes the carry flag to be undefined.
Table 3-3 Carry Flag Manipulation Instructions
Instruction (mnemonic)
Instruction dedicated to
SET1 CY
carry flag manipulation
CLR1 CY
NOT1 CY
SKT CY
Bit transfer instruction
MOV1 mem*.bit CY
MOV1 CY,mem*.bit
Bit Boolean instruction
AND1 CY,mem*.bit
OR1 CY,mem*.bit
XOR1 CY,mem*.bit
Interrupt handling
Interrupt execution
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
RETI
Remark
mem*.bit represents the following three addressing modes:
• fmem.bit
• pmem.@L
• @H+mem.bit
(2) Skip flags (SK2, SK1, SK0)
The skip flags are used to store skip status, and are automatically set or reset when the CPU executes an
instruction.
The user cannot directly manipulate these flags as operands.
36
Carry flag operation/processing
Sets CY to 1.
Clears CY to 0.
Inverts the contents of CY.
Skips if CY is set to 1.
Transfers the contents of CY to a specified bit.
Transfers the contents of a specified bit to CY.
ANDs, ORs, or XORs CY with the contents of a specified bit, then
sets the result in CY.
Saves CY and all other PSW bits to stack memory in parallel.
Restores CY together with the other PSW bits from stack memory.
PD75238