AT89LP2052 datasheet(20/90 Pages) ATMEL

20 / 90 page

3547F–MICRO–6/06

AT89LP2052/LP4052

14.6

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 14-2 for a complete list of Read-Modify-Write instruction which may access the ports.

14.7

Port Alternate Functions

Most general-purpose digital I/O pins of the AT89LP2052/LP4052 share functionality with the

various I/Os needed for the peripheral units. Table 14-4 lists the alternate functions of the port

pins. Alternate functions are connected to the pins in a logic AND fashion. In order to enable the

alternate function on a port pin, that pin must have a “1” in its corresponding port register bit, oth-

erwise, the input/output will always be “0”. Furthermore, each pin must be configured

for the correct input/output mode as required by its peripheral before it may be used as such.

Table 14-3 shows how to configure a generic pin for use with an alternate function.

Table 14-2.

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

Table 14-3.

Alternate Function Configurations for Pin y of Port x

PxM0.y

PxM1.y

Px.y

I/O Mode

Bidirectional (internal pull-up)

011

Output

Input

Bidirectional (external pull-up)

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