UPSD3422 datasheet(29/293 Pages) STMICROELECTRONICS

29 / 293 page

uPSD34xx

8032 MCU registers

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the B Register to hold 16-bit operands. The ACC is referred to as “A” in the MCU instruction

set.

7.5

B register (B)

The B Register is a general purpose 8-bit register for temporary data storage and also used

as a 16-bit register when concatenated with the ACC Register for use with MUL and DIV

instructions.

7.6

General purpose registers (R0 - R7)

There are four banks of eight general purpose 8-bit registers (R0 - R7), but only one bank of

eight registers is active at any given time depending on the setting in the PSW word

(described next). R0 - R7 are generally used to assist in manipulating values and moving

data from one memory location to another. These register banks physically reside in the first

32 locations of 8032 internal DATA SRAM, starting at address 00h. At reset, only the first

bank of eight registers is active (addresses 00h to 07h), and the stack begins at address

08h.

7.7

Program status word (PSW)

The PSW is an 8-bit register which stores several important bits, or flags, that are set and

cleared by many 8032 instructions, reflecting the current state of the MCU core. Figure 12

on page 30 shows the individual flags.

7.7.1

Carry flag (CY)

This flag is set when the last arithmetic operation that was executed results in a carry

(addition) or borrow (subtraction). It is cleared by all other arithmetic operations. The CY flag

is also affected by Shift and Rotate Instructions.

7.7.2

Auxiliary carry flag (AC)

This flag is set when the last arithmetic operation that was executed results in a carry into

(addition) or borrow from (subtraction) the high-order nibble. It is cleared by all other

arithmetic operations.

7.7.3

General purpose flag (F0)

This is a bit-addressable, general-purpose flag for use under software control.

7.7.4

These bits select which bank of eight registers is used during R0 - R7 register accesses

(see Table 4)

7.7.5

Overflow flag (OV)

The OV flag is set when: an ADD, ADDC, or SUBB instruction causes a sign change; a MUL

instruction results in an overflow (result greater than 255); a DIV instruction causes a divide-

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