Siemens EF 88H Series Bedienungsanleitung PDF herunterladen (Seite 19)

Fundamental Structure

C501

Semiconductor Group 2-3

Special Function Register PSW (Address D0

) Reset Value : 00

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 07

after a reset. This causes the stack to begin

a location = 08

above register bank zero. The SP can be read or written under software control.

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

RS0

These bits are used to select one of the four register banks.

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.

CY AC

RS1 RS0 OV F1 PD0

PSW

Bit No. MSB LSB

RS1 RS0 Function

0 0 Bank 0 selected, data address 00

-07

0 1 Bank 1 selected, data address 08

-0F

1 0 Bank 2 selected, data address 10

-17

1 1 Bank 3 selected, data address 18

-1F

1 2 ... 14 15 16 17 18 19 20 21 22 23 24 ... 120 121

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