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The 8051 Instruction Set

Atmel 8051 Microcontrollers Hardware Manual 1-38

4316E–8051–01/07

1.14.17 INC DPTR

1.14.18 JB blt,rel

Function: Increment Data Pointer

Description: INC DPTR increments the 16-bit data pointer by 1. A 16-bit increment (modulo 2

) is performed, and an

overflow of the low-order byte of the data pointer (DPL) from 0FFH to 00H increments the high-order byte (DPH).

No flags are affected.

This is the only 16-bit register which can be incremented.

Example: Registers DPH and DPL contain 12H and 0FEH, respectively. The following instruction sequence,

INC DPTR

changes DPH and DPL to 13H and 01H.

Bytes: 1

Cycles: 2

Encoding: 1 0 1 0 0 0 1 1

Operation: INC

(DPTR) ← (DPTR) + 1

Function: Jump if Bit set

Description: If the indicated bit is a one, JB jump to the address indicated; otherwise, it proceeds with the next instruction.

The branch destination is computed by adding the signed relative-displacement in the third instruction byte to the

PC, after incrementing the PC to the first byte of the next instruction. The bit tested is not modified. No flags are

affected.

Example: The data present at input port 1 is 11001010B. The Accumulator holds 56 (01010110B). The following instruction

sequence,

JB P1.2,LABEL1

JB ACC. 2,LABEL2

causes program execution to branch to the instruction at label LABEL2.

Bytes: 3

Cycles: 2

Encoding: 0 0 1 0 0 0 0 0 bit address rel. address

Operation: JB

(PC) ← (PC) + 3

IF (bit) = 1

THEN

(PC) ← (PC) + rel

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Atmel C51 Handbuch Seite 40