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80515 mpu, Accumulator, The b register – Maxim Integrated 71M6513H Power Meter IC Family Software User Manual

Page 115: Program status word (psw)

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71M651x Software User’s Guide

6.3.2. 80515 MPU

The 80515 MPU is composed of four components:

1.

Control unit

2.

Arithmetic-logic unit

3.

Memory control unit

4.

RAM and SFR control unit

The 80515 MPU allows instruction fetch from program memory and instruction execution using RAM or SFR. The
following chapter describes the main MPU registers.

Accumulator

ACC is the accumulator register. Most instructions use the accumulator to hold the operand. The mnemonics for
accumulator-specific instructions refer to accumulator as “A”, not ACC.

The B Register

The B register is used during multiply and divide instructions. It can also be used as a scratch-pad register to hold
temporary data.

Program Status Word (PSW)

MSB

LSB

CV

AC

F0

RS1

RS

OV

-

P

Table 6-17: PSW Register Flags

Bit

Symbol

Function

PSW.7

CV

Carry flag

Psw.6

AC

Auxiliary Carry flag for BCD operations

PSW.5

F0

General purpose Flag 0 available for user

PSW.4

RS1

PSW.3

RS0

Register bank select control bits. The contents of rs1 and rs0 select the working
register bank as follows:

(0, 0): Bank 0 (0x00-0x07)
(0,1): Bank 1 (0x08-0x0F)
(1, 0): Bank 2 (0x10-0x17)
(1, 1): Bank 3 (0x18-0x1F)

PSW.2

OV

Overflow flag

PSW.1

-

User defined flag

PSW.0

P

Parity flag, affected by hardware to indicate odd / even number of “one” bits in the
Accumulator, i.e. even parity.

Table 6-18: PSW Bit Functions

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