AT89LP51 datasheet(44/113 Pages) ATMEL

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3709C–MICRO–5/11

AT89LP51/52 - Preliminary

10.1.4

Push-pull Output

The push-pull output configuration has the same pull-down structure as both the open-drain and

the quasi-bidirectional output modes, but provides a continuous strong pull-up when the port

latch contains a logic “1”. The push-pull mode may be used when more source current is needed

from a port output. The push-pull port configuration is shown in Figure 10-5.

Figure 10-5. Push-pull Output

10.2

Port Read-Modify-Write

A read from a port will read either the state of the pins or the state of the port register depending

on which instruction is used. Simple read instructions will always access the port pins directly.

Read-modify-write instructions, which read a value, possibly modify it, and then write it back, will

always access the port register. This includes bit write instructions such as CLR or SETB as they

actually read the entire port, modify a single bit, then write the data back to the entire port. See

Table 10-4 for a complete list of Read-Modify-Write instruction which may access the ports.

Port

VCC

From Port

Input

Data

PWD

Table 10-4.

Port Read-Modify-Write Instructions

Mnemonic

Instruction

Example

ANL

Logical AND

ANL P1, A

ORL

Logical OR

ORL P1, A

XRL

Logical EX-OR

XRL P1, A

JBC

Jump if bit set and clear bit

JBC P3.0, LABEL

CPL

Complement bit

CPL P3.1

INC

Increment

INC P1

DEC

Decrement

DEC P3

DJNZ

Decrement and jump if not zero

DJNZ P3, LABEL

MOV PX.Y, C

Move carry to bit Y of Port X

MOV P1.0, C

CLR PX.Y

Clear bit Y of Port X

CLR P1.1

SETB PX.Y

Set bit Y of Port X

SETB P3.2

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