MC68HC705P9 Datasheet, PDF (38/156 Pages) Motorola, Inc – HCMOS Microcontroller Unit

CPU _{CPU Registers}
The 10 most significant bits of the stack pointer are permanently fixed at
0000000011, so the stack pointer produces addresses from $00C0 to
$00FF. If subroutines and interrupts use more than 64 stack locations,
the stack pointer wraps around to address $00FF and begins writing
over the previously stored data. A subroutine uses two stack locations;
an interrupt uses five locations.
Program Counter
The program counter is a 16-bit register that contains the address of the
next instruction or operand to be fetched. The three most significant bits
of the program counter are ignored internally and appear as 000.
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.
Bit
15 14 13 12 11 10 9 8 7 6 5 4 3 2
Read:
Write:
Reset: 0 0 0
Loaded with vector from $1FFE and $1FFF
Figure 5. Program Counter (PC)
Bit
10
Condition Code
Register
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.
Bit 7
6
5
4
3
2
1
Bit 0
Read: 1
1
1
H
I
N
Z
C
Write:
Reset: 1
1
1
U
1
U
U
U
= Unimplemented
U = Unaffected
Figure 6. Condition Code Register (CCR)
6-hc05cpu
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CPU
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