C515A_9708 Datasheet, PDF (17/182 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

Fundamental Structure
C515A
Special Function Register PSW (Address D0H)
Reset Value : 00H
Bit No. MSB
D7H
D0H CY
D6H
AC
D5H
F0
D4H
RS1
D3H
RS0
D2H
OV
D1H
F1
LSB
D0H
P
PSW
Bit
Function
CY
Carry Flag
Used by arithmetic instruction.
AC
Auxiliary Carry Flag
Used by instructions which execute BCD operations.
F0
General Purpose Flag
RS1
Register Bank Select Control Bits
RS0
These bits are used to select one of the four register banks.
RS1
RS0
Function
0
0
Bank 0 selected, data address 00H-07H
0
1
Bank 1 selected, data address 08H-0FH
1
0
Bank 2 selected, data address 10H-17H
1
1
Bank 3 selected, data address 18H-1FH
OV
Overflow Flag
Used by arithmetic instruction.
F1
General Purpose Flag
P
Parity Flag
Set/cleared by hardware after each instruction to indicate an odd/even
number of "one" bits in the accumulator, i.e. even parity.
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, i.e. 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 07H after a reset. This causes the stack to begin
a location = 08H above register bank zero. The SP can be read or written under software control.
Semiconductor Group
2-3
1997-08-01