SZF2002 datasheet(16/76 Pages) PHILIPS

16 / 76 page

1998 Aug 26

Philips Semiconductors

Product speciﬁcation

Low voltage 8-bit microcontroller with

6-kbyte embedded RAM

SZF2002

10 PROGRAM STATUS WORD (PSW)

The Program Status Word contains several status bits that

reflect the current state of the CPU. The PSW, shown in

Table 4, resides in the SFR memory space. It contains the

Carry bit, the Auxiliary Carry (for BCD operations), the two

two user-definable status flags.

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.

Bits RS0 and RS1 are used to select one of the four

to these RAM locations as R0 through to R7. The selection

of which of the four register banks is being referred to is

made on the basis of the state of RS0 and RS1 at

execution time.

The Parity bit reflects the number of 1s in the Accumulator:

P = 1, if the Accumulator contains an odd number of 1s,

and P = 0, if the Accumulator contains an even number of

1s. Thus, the number of 1s in the Accumulator plus P is

always even. The bits F0 and USR are uncommitted and

may be used as general purpose status flags.

Table 4

Program Status Word (SFR address D0H)

Table 5

Description of PSW bits

76543210

RS1

RS0

USR

BIT

SYMBOL

DESCRIPTION

7CY

Carry ﬂag. The Carry ﬂag receives carry out from bit 7 of ALU operands.

6AC

Auxiliary Carry ﬂag. The Auxiliary Carry ﬂag receives carry out from bit 3 of addition

operands.

5F0

General purpose status ﬂag.

RS1

RS0

2OV

Overﬂow ﬂag. This ﬂag is set by arithmetic operations.

USR

USR. This is a user-deﬁnable ﬂag.

Parity. If the Accumulator contains an odd number of 1s this bit is set to a logic 1 by

hardware. Otherwise, the state of this bit is a logic 0.

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