Fundamental Structure
C513AO
User’s Manual
2-3
05.99
Special Function Register PSW (Address D0
H
)
Reset Value: 00
H
B Register
The B Register is used during multiply and divide and serves as both source and destination. For
other instructions, it can be treated as another scratch pad register.
Stack Pointer
The Stack Pointer (SP) Register is 8 bits wide. It is incremented before data is stored during PUSH
and CALL executions and decremented after data is popped during a POP and RET (RETI)
execution. That is, it always points to the last valid stack byte. While the stack may reside anywhere
in the on-chip RAM, the stack pointer is initialized to 07
H
after a reset. This causes the stack to begin
at location = 08
H
above Register Bank 0. The SP can be read or written by software.
Bit
Function
CY
Carry Flag
Used by arithmetic instruction.
AC
Auxiliary Carry Flag
Used by instructions which execute BCD operations.
F0
General Purpose Flag 0
RS1
RS0
Register bank Select control bits
These bits are used to select one of the four register banks.
OV
Overflow Flag
Used by arithmetic instruction.
F1
General Purpose Flag 1
P
Parity Flag
Set or cleared by hardware after each instruction to indicate an odd or even
number of 1 bits in the Accumulator. A “1” indicates odd parity while a “0”
indicates even parity.
CY
AC
F0
RS1
RS0
OV
F1
P
D0
H
PSW
D7
H
D6
H
D5
H
D4
H
D3
H
D2
H
D1
H
D0
H
Bit No.
MSB
LSB
RS1
RS0
Function
0
0
Bank 0 selected, data address 00
H
-07
H
0
1
Bank 1 selected, data address 08
H
-0F
H
1
0
Bank 2 selected, data address 10
H
-17
H
1
1
Bank 3 selected, data address 18
H
-1F
H