mc68hc05x4dw Freescale Semiconductor, Inc, mc68hc05x4dw Datasheet - Page 30

• Manufacturer Part Number: mc68hc05x4dw
• Description: Xc68hc705x4 Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

Program Counter
Condition Code
Register
CPU
MC68HC05X4
Reset
Reset
Bit 15 14
–
–
The program counter is a 16-bit register that contains the address of the
next instruction or operand to be fetched. The two most significant bits
of the program counter are ignored internally.
Normally, the address in the program counter automatically increments
to the next sequential memory location every time an instruction or
operand is fetched. Jump, branch, and interrupt operations load the
program counter with an address other than that of the next sequential
location.
The condition code register is an 8-bit register whose three most
significant bits are permanently fixed at 111. The condition code register
contains the interrupt mask and four flags that indicate the results of the
instruction just executed. The following paragraphs describe the
functions of the condition code register.
Half-Carry Flag
The CPU sets the half-carry flag when a carry occurs between bits 3 and
4 of the accumulator during an ADD or ADC operation. The half-carry
flag is required for binary-coded decimal (BCD) arithmetic operations.
Interrupt Mask
Setting the interrupt mask disables interrupts. If an interrupt request
occurs while the interrupt mask is logic zero, the CPU saves the CPU
registers on the stack, sets the interrupt mask, and then fetches the
Bit 7
1
1
Freescale Semiconductor, Inc.
–
–
For More Information On This Product,
13
6
1
1
Figure 6. Condition Code Register
12
Go to: www.freescale.com
Figure 5. Program Counter
11
5
1
1
10
CPU
Loaded with vector from $3FFE AND $3FFF
9
H
U
4
8
7
3
1
I
6
5
N
U
2
4
3
C
U
1
2
1
Bit 0
U
Z
Bit 0
4-cpu