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Maxim Integrated 19-9

MAX31782 User’s Guide

Revision 0; 8/11

19.5.5 ALU Bit Operations Using Only the Active Accumulator

The following operations operate on single bits of the current active accumulator in conjunction with the Carry flag. Any

of these operations may use an Acc bit from 0 to 15.

move C,Acc.0 ;copybit0ofaccumulatortoCarry

move Acc.5,C ;copyCarrytobit5ofaccumulator

and Acc.3  ;Acc.3=Acc.3ANDCarry

or Acc.0  ;Acc.0=Acc.0ORCarry

xor Acc.1  ;Acc.1=Acc.1ORCarry

None of the above bit operations cause the auto-increment, auto-decrement, or modulo operations defined by the

accumulator pointer control (APC) register.

19.5.6 Example: Adding Two 4-Byte Numbers Using Auto-Increment

move A[0],#5678h;Firstnumber–12345678h

move A[1],#1234h

move A[2],#0AAAAh;Secondnumber–0AAAAAAAh

move A[3],#0AAAh

move APC,#81h ;ActiveAcc=A[0],incrementlowbit=mod2

add A[2]  ;A[0]=5678h+AAAAh=0122h+Carry

addc A[3]  ;A[1]=1234h+AAAh+1=1CDFh

    ;12345678h+0AAAAAAAh=1CDF0122h

9.6 Processor Status Flag Operations

The Processor Status Flag (PSF) register contains five flags that are used to indicate and store the results of arithmetic

and logical operations, four of which can also be used for conditional program branching.

19.6.1 Sign Flag

The Sign flag (PSF.6) reflects the current state of the most significant bit of the active accumulator. If signed arithmetic

is being used, this flag indicates whether the value in the accumulator is positive or negative.

Since the Sign flag is a dynamic reflection of the high bit of the active accumulator, any instruction that changes the

value in the active accumulator can potentially change the value of the Sign flag. Also, any instruction that changes

which accumulator is the active one (including AP auto-increment/decrement) can also change the Sign flag.

The following operation uses the Sign flag:

• JUMP S, src (Jump if Sign flag is set)

19.6.2 Zero Flag

The Zero flag (PSF.7) is a dynamic flag that reflects the current state of the active accumulator Acc. If all bits in the

active accumulator are zero, the Zero flag equals 1. Otherwise, it equals 0.

Since the Zero flag is a dynamic reflection of (Acc = 0), any instruction that changes the value in the active accumulator

can potentially change the value of the Zero flag. Also, any instruction that changes which accumulator is the active one

(including AP auto-increment/decrement) can also change the Zero flag.

The following operations use the Zero flag:

• JUMP Z, src (Jump if Zero flag is set)

• JUMP NZ, src (Jump if Zero flag is cleared)

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MAX31782 User’s Guide 1

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