MC9S08GB60 Datasheet, PDF (129/290 Pages) Motorola, Inc – Microcontrollers

Programmer’s Model and CPU Registers
V — Two’s Complement Overflow Flag
The CPU sets the overflow flag when a two’s complement overflow occurs. The signed branch
instructions BGT, BGE, BLE, and BLT use the overflow flag.
1 = Overflow
0 = No overflow
H — Half-Carry Flag
The CPU sets the half-carry flag when a carry occurs between accumulator bits 3 and 4 during an
add-without-carry (ADD) or add-with-carry (ADC) operation. The half-carry flag is required for
binary-coded decimal (BCD) arithmetic operations. The DAA instruction uses the states of the H and
C condition code bits to automatically add a correction value to the result from a previous ADD or
ADC on BCD operands to correct the result to a valid BCD value.
1 = Carry between bits 3 and 4
0 = No carry between bits 3 and 4
I — Interrupt Mask Bit
When the interrupt mask is set, all maskable CPU interrupts are disabled. CPU interrupts are enabled
when the interrupt mask is cleared. When a CPU interrupt occurs, the interrupt mask is set
automatically after the CPU registers are saved on the stack, but before the first instruction of the
interrupt service routine is executed.
1 = Interrupts disabled
0 = Interrupts enabled
Interrupts are not recognized at the instruction boundary after any instruction that clears I (CLI or
TAP). This ensures that the next instruction after a CLI or TAP will always be executed without the
possibility of an intervening interrupt, provided I was set.
N — Negative Flag
The CPU sets the negative flag when an arithmetic operation, logic operation, or data manipulation
produces a negative result, setting bit 7 of the result. Simply loading or storing an 8-bit or 16-bit value
causes N to be set if the most significant bit of the loaded or stored value was 1.
1 = Negative result
0 = Non-negative result
Z — Zero Flag
The CPU sets the zero flag when an arithmetic operation, logic operation, or data manipulation
produces a result of $00 or $0000. Simply loading or storing an 8-bit or 16-bit value causes Z to be set
if the loaded or stored value was all 0s.
1 = Zero result
0 = Non-zero result
C — Carry/Borrow Flag
The CPU sets the carry/borrow flag when an addition operation produces a carry out of bit 7 of the
accumulator or when a subtraction operation requires a borrow. Some instructions — such as bit test
and branch, shift, and rotate — also clear or set the carry/borrow flag.
1 = Carry out of bit 7
0 = No carry out of bit 7
MC9S08GB/GT Data Sheet, Rev. 2.3
Freescale Semiconductor
129