DS80C320 datasheet(12/42 Pages) DALLAS

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DS80C320/DS80C323

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DUAL DATA POINTER

Data memory block moves can be accelerated using the Dual Data Pointer (DPTR). The standard 8032

DPTR is a 16-bit value that is used to address off-chip data RAM or peripherals. In the

DS80C320/DS80C323, the standard 16-bit data pointer is called DPTR0 and is located at SFR addresses

82h and 83h. These are the standard locations. The new DPTR is located at SFR 84h and 85h and is

called DPTR1. The DPTR Select bit (DPS) chooses the active pointer and is located at the LSB of the

SFR location 86h. No other bits in register 86h have any effect and are set to 0. The user switches

between data pointers by toggling the LSB of register 86h. The increment (INC) instruction is the fastest

way to accomplish this. All DPTR-related instructions use the currently selected DPTR for any activity.

Therefore only one instruction is required to switch from a source to a destination address. Using the

Dual-Data Pointer saves code from needing to save source and destination addresses when doing a block

move. Once loaded, the software simply switches between DPTR and 1. The relevant register locations

are as follows.

DPL

82h

Low byte original DPTR

DPH

83h

High byte original DPTR

DPL1

84h

Low byte new DPTR

DPH1

85h

High byte new DPTR

DPS

86h

DPTR Select (LSB)

Sample code listed below illustrates the saving from using the dual DPTR. The example program was

original code written for an 8051 and requires a total of 1869 DS80C320/DS80C323 machine cycles. This

takes 299 µs to execute at 25 MHz. The new code using the Dual DPTR requires only 1097 machine

cycles taking 175.5 µs. The Dual DPTR saves 772 machine cycles or 123.5 µs for a 64-byte block move.

Since each pass through the loop saves 12 machine cycles when compared to the single DPTR approach,

larger blocks gain more efficiency using this feature.

64-BYTE BLOCK MOVE WITHOUT DUAL DATA POINTER

; SH and SL are high and low byte source address.

; DH and DL are high and low byte of destination address.

# CYCLES

MOV

R5, #64d

; NUMBER OF BYTES TO MOVE

MOV

DPTR, #SHSL

; LOAD SOURCE ADDRESS

MOV

R1, #SL

; SAVE LOW BYTE OF SOURCE

MOV

R2, #SH

; SAVE HIGH BYTE OF SOURCE

MOV

R3, #DL

; SAVE LOW BYTE OF DESTINATION

MOV

R4, #DH

; SAVE HIGH BYTE OF DESTINATION

MOVE:

; THIS LOOP IS PERFORMED THE NUMBER OF TIMES LOADED INTO R5, IN THIS EXAMPLE 64

MOVX

A, @DPTR

; READ SOURCE DATA BYTE

MOV

R1, DPL

; SAVE NEW SOURCE POINTER

MOV

R2, DPH

;

MOV

DPL, R3

; LOAD NEW DESTINATION

MOV

DPH, R4

;

MOVX

@DPTR, A

; WRITE DATA TO DESTINATION

INC

DPTR

; NEXT DESTINATION ADDRESS

MOV

R3, DPL

; SAVE NEW DESTINATION POINTER

MOV

R4, DPH

;

MOV

DPL, R1

; GET NEW SOURCE POINTER

MOV

DPH, R2

;

INC

DPTR

; NEXT SOURCE ADDRESS

DJNZ

R5, MOVE

; FINISHED WITH TABLE?

DS80C320 Datasheet(PDF) 12 Page - Dallas Semiconductor

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