STC89C53RC datasheet(34/165 Pages) STC

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Program Status Word(PSW)

The program status word(PSW) contains several status bits that reflect the current state of the CPU. The PSW,

shown below, resides in the SFR space. It contains the Carry bit, the Auxiliary Carry(for BCD operation), the two

The Carry bit, other than serving the function of a Carry bit in arithmetic operations, also serves as the

“Accumulator” for a number of Boolean operations.

The bits RS0 and RS1 are used to select one of the four register banks shown in the previous page. A number of

instructions refer to these RAM locations as R0 through R7.

The Parity bit reflects the number of 1s in the Accumulator. P=1 if the Accumulator contains an odd number of 1s

and otherwise P=0.

PSW register

bit

76543210

name

RS1

RS0

CY : Carry flag.

AC : Auxilliary Carry Flag.(For BCD operations)

F0 : Flag 0.(Available to the user for general purposes)

RS1: Register bank select control bit 1.

RS0: Register bank select control bit 0.

OV : Overflow flag.

F1 : Flag 1. User-defined flag.

: Parity flag.

Data Pointer

The Data Pointer (DPTR) consists of a high byte (DPH) and a low byte (DPL). Its intended function is to hold a

16-bit address. It may be manipulated as a 16-bit register or as two independent 8-bit registers.

For fast data movement, STC89xx series support two data pointers. They share the same SFR address and are

switched by the register bit – DPS/AUXR1.0.

AUXR1 register

LSB

bit

name

GF2

DPS

GF2 : General purpose user defined flag. It can be used by software.

DPS : DPTR registers select bit.

0 : DPTR0 is selected(Default).

1 : The secondary DPTR(DPTR 1) is switched to use.

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