Motorola MC6805R Series Advance Information page 27

SECTION 4
PROGRAMMABLE REGISTERS
The M6805 Family CPU has five registers available to the programmer. They are shown in Figure 4-1
and are explained in the following paragraphs.
7
0
I
A
I
Accumulator
0
I
X
I
Index Register
11
8 7
0
I
PCH
1
PCl 1
Program Counter
11
54
0
101010101011111
SP
I
Stack Pointer
4
0
Condition Code Register
'--r-...L....r--'--r....L....,r-'-~
4.1 ACCUMULATOR (A)
Carry / Borrow
Zero
L----Negative
L-----Interrupt Mask
L....------Half Carry
Figure 4-1. Programming Model
The accumulator is a general purpose 8-bit register used to hold operands and results of arithmetic
calculations or data manipulations.
4.2 INDEX REGISTER (X)
The index register is an 8-bit register used for the indexed addressing mode. It contains an 8-bit
value that may be added to an 8- or 16-bit immediate value to create an effective address. The index
register may also be used as a temporary storage area.
4.3 PROGRAM COUNTER (PC)
The program counter is a 12-bit register that contains the address of the next bye to be fetched.
4-1