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Maxim Integrated 19-4

MAX31782 User’s Guide

Revision 0; 8/11

19.3.4 Moving Values Between Registers of Different Sizes

Before covering some transfer scenarios that might arise, a special register must be introduced that will be used in

many of these cases. The 16-bit General Register (GR) is expressly provided for performing byte singulation of 16-bit

words. The high and low bytes of GR are individually accessible in the GRH and GRL registers respectively. A read-

only GRS register makes a byte-swapped version of GR accessible and the GRXL register provides a sign-extended

version of GRL.

8-bit destination ← low byte (16-bit source)

The simplest transfer possibility would be loading an 8-bit register with the low byte of a 16-bit register. This transfer

does not require use of GR and requires a prefix only if the destination or source register are outside of the single cycle

write or read regions, 0–7h and 0–Fh, respectively.

move OFFS,LC[0] ;copythelowbyteofLC[0]totheOFFSregister

move IMR,@DP[1] ;copythelowbyte@DP[1]totheIMRregister

move WDCN,LC[0] ;assemblesto: movePFX[2],#00h

    ;   move(WDCON-80h),LC[0]

8-bit destination ← high byte (16-bit source)

If, however, we needed to load an 8-bit register with the high byte of a 16-bit source, it would be best to use the GR

move GR,LC[0] ;moveLC[0]totheGRregister

move IC,GRH ;copythehighbyteintotheICregister

16-bit destination ← concatenation (8-bit source, 8-bit source)

Two 8-bit source registers can be concatenated and stored into a 16-bit destination by using the prefix register to hold

the high-order byte for the concatenated transfer. An additional cycle may be required if either source byte register

index is greater than 0Fh or the 16-bit destination is greater than 07h.

move PFX[0],IC ;loadhighordersourcebyteICintoPFX

move @++SP,AP ;store@DP[0]theconcatenationofIC:AP

    ;16-bitdestinationsub-index:dst=08h

    ;8-bitsourcesub-indexes:

    ;high=10h,low=11h

move PFX[1],#00h;

move PFX[3],high;PFX=00:high

move dst,low ;dst=high:low

Low (16-bit destination) ← 8-bit source

To modify only the low byte of a given 16-bit destination, the 16-bit register should be moved into the GR register such

that the high byte can be singulated and the low byte written exclusively. An additional cycle is required if the destina-

tion index is greater than 0Fh.

move GR,DP[0] ;moveDP[0]totheGRregister

move PFX[0],GRH ;getthehighbyteofDP[0]viaGRH

move DP[0],#20h ;storethenewDP[0]value

    ;16-bitdestinationsub-index:dst=10h

    ;8-bitsourcesub-index:src=11h

move PFX[1],#00h;

move GR,dst ;readdstwordtotheGRregister

move PFX[5],GRH ;getthehighbyteofdstviaGRH

move dst,src ;storethenewdstvalue

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