
Central Processor Unit (CPU)
CPU Registers
M68HC11E Family — Rev. 5
Data Sheet
MOTOROLA
Central Processor Unit (CPU)
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4.2.6  Condition Code Register (CCR) 
This 8-bit register contains:
Five condition code indicators (C, V, Z, N, and H),
Two interrupt masking bits (IRQ and XIRQ)
A stop disable bit (S)
In the M68HC11 CPU, condition codes are updated automatically by most 
instructions. For example, load accumulator A (LDAA) and store accumulator A 
(STAA) instructions automatically set or clear the N, Z, and V condition code flags. 
Pushes, pulls, add B to X (ABX), add B to Y (ABY), and transfer/exchange 
instructions do not affect the condition codes. Refer to 
Table 4-2
, which shows 
what condition codes are affected by a particular instruction. 
4.2.6.1  Carry/Borrow (C) 
The C bit is set if the arithmetic logic unit (ALU) performs a carry or borrow during 
an arithmetic operation. The C bit also acts as an error flag for multiply and divide 
operations. Shift and rotate instructions operate with and through the carry bit to 
facilitate multiple-word shift operations. 
4.2.6.2  Overflow (V) 
The overflow bit is set if an operation causes an arithmetic overflow. Otherwise, the 
V bit is cleared. 
4.2.6.3  Zero (Z) 
The Z bit is set if the result of an arithmetic, logic, or data manipulation operation 
is 0. Otherwise, the Z bit is cleared. Compare instructions do an internal implied 
subtraction and the condition codes, including Z, reflect the results of that 
subtraction. A few operations (INX, DEX, INY, and DEY) affect the Z bit and no 
other condition flags. For these operations, only = and 
≠
 conditions can be 
determined. 
4.2.6.4  Negative (N) 
The N bit is set if the result of an arithmetic, logic, or data manipulation operation 
is negative (MSB = 1). Otherwise, the N bit is cleared. A result is said to be negative 
if its most significant bit (MSB) is a 1. A quick way to test whether the contents of a 
memory location has the MSB set is to load it into an accumulator and then check 
the status of the N bit. 
4.2.6.5  Interrupt Mask (I) 
The interrupt request (IRQ) mask (I bit) is a global mask that disables all maskable 
interrupt sources. While the I bit is set, interrupts can become pending, but the 
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.