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The 8051 Instruction Set

1-47 Atmel 8051 Microcontrollers Hardware Manual

4316E–8051–01/07

1.14.30 MOV DPTR,#data16

1.14.31 MOVC A,@A+

<base-reg>

Function: Load Data Pointer with a 16-bit constant

Description: MOV DPTR,#data16 loads the Data Pointer with the 16-bit constant indicated. The 16-bit constant is loaded into

the second and third bytes of the instruction. The second byte (DPH) is the high-order byte, while the third byte

(DPL) holds the lower-order byte. No flags are affected.

This is the only instruction which moves 16 bits of data at once.

Example: The instruction,

MOV DPTR, # 1234H

loads the value 1234H into the Data Pointer: DPH holds 12H, and DPL holds 34H.

Bytes: 3

Cycles: 2

Encoding: 1 0 0 1 0 0 0 0 immed. data15-8 immed. data7-0

Operation: MOV

(DPTR) ← #data

15-0

DPH ← DPL ← #data

15-8

← #data

7-0

Function: Move Code byte

Description: The MOVC instructions load the Accumulator with a code byte or constant from program memory. The address

of the byte fetched is the sum of the original unsigned 8-bit Accumulator contents and the contents of a 16-bit

base register, which may be either the Data Pointer or the PC. In the latter case, the PC is incremented to the

address of the following instruction before being added with the Accumulator; otherwise the base register is not

altered. Sixteen-bit addition is performed so a carry-out from the low-order eight bits may propagate through

higher-order bits. No flags are affected.

Example: A value between 0 and 3 is in the Accumulator. The following instructions will translate the value in the

Accumulator to one of four values defined by the DB (define byte) directive.

REL_PC: INC A

MOVC A,@A+PC

RET

DB 66H

DB 77H

DB 88H

DB 99H

If the subroutine is called with the Accumulator equal to 01H, it returns with 77H in the Accumulator. The INC A

before the MOVC instruction is needed to “get around” the RET instruction above the table. If several bytes of

code separate the MOVC from the table, the corresponding number is added to the Accumulator instead.

1 2 ... 44 45 46 47 48 49 50 51 52 53 54 ... 115 116

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