AT89LP428-20MU ATMEL [ATMEL Corporation], AT89LP428-20MU Datasheet - Page 39

• Manufacturer Part Number: AT89LP428-20MU
• Description: 8-bit Microcontroller with 4K/8K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

10.3
10.4
3654A–MICRO–8/09
Port Read-Modify-Write
Port Alternate Functions
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
Table 10-4.
Most general-purpose digital I/O pins of the AT89LP428/828 share functionality with the various
I/Os needed for the peripheral units.
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,
otherwise the input/output will always be “0”. However, alternate functions may be temporarily
forced to “0” by clearing the associated port bit, provided that the pin is not in input-only mode.
Furthermore, each pin must be configured for the correct input/output mode as required by its
peripheral before it may be used as such.
use with an alternate function.
Table 10-5.
Mnemonic
ANL
ORL
XRL
JBC
CPL
INC
DEC
DJNZ
MOV PX.Y, C
CLR PX.Y
SETB PX.Y
PxM0.y
0
0
1
1
for a complete list of Read-modify-write instructions which may access the ports.
Port Read-Modify-Write Instructions
Alternate Function Configurations for Pin y of Port x
Instruction
Logical AND
Logical OR
Logical EX-OR
Jump if bit set and clear bit
Complement bit
Increment
Decrement
Decrement and jump if not zero
Move carry to bit Y of Port X
Clear bit Y of Port X
Set bit Y of Port X
PxM1.y
0
1
0
1
Table 10-6
Table 10-5
Px.y
X
lists the alternate functions of the port pins.
1
1
1
shows how to configure a generic pin for
Bidirectional (internal pull-up)
Output
Input
Bidirectional (external pull-up)
I/O Mode
AT89LP428/828
Example
ANL P1, A
ORL P1, A
XRL P1, A
JBC P3.0, LABEL
CPL P3.1
INC P1
DEC P3
DJNZ P3, LABEL
MOV P1.0, C
CLR P1.1
SETB P3.2
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