at89c51ac3-s3sim ATMEL Corporation, at89c51ac3-s3sim Datasheet - Page 6

• Manufacturer Part Number: at89c51ac3-s3sim
• Description: At89c51ac3 Enhanced 8-bit Microcontroller With 64kb Flash Memory
• Manufacturer: ATMEL Corporation

6
Pin Name
P3.0:7
P4.0:4
AT89C51AC3
Type
I/O
I/O
Description
Port 3:
Is an 8-bit bi-directional I/O port with internal pull-ups. Port 3 pins that have 1’s written to them are pulled high by the internal
pull-up transistors and can be used as inputs in this state. As inputs, Port 3 pins that are being pulled low externally will be a
source of current (I
The output latch corresponding to a secondary function must be programmed to one for that function to operate (except for
TxD and WR). The secondary functions are assigned to the pins of port 3 as follows:
P3.0/RxD:
Receiver data input (asynchronous) or data input/output (synchronous) of the serial interface
P3.1/TxD:
Transmitter data output (asynchronous) or clock output (synchronous) of the serial interface
P3.2/INT0:
External interrupt 0 input/timer 0 gate control input
P3.3/INT1:
External interrupt 1 input/timer 1 gate control input
P3.4/T0:
Timer 0 counter input
P3.5/T1/SS:
Timer 1 counter input
SPI Slave Select
P3.6/WR:
External Data Memory write strobe; latches the data byte from port 0 into the external data memory
P3.7/RD:
External Data Memory read strobe; Enables the external data memory.
It can drive CMOS inputs without external pull-ups.
Port 4:
Is an 2-bit bi-directional I/O port with internal pull-ups. Port 4 pins that have 1’s written to them are pulled high by the internal
pull-ups and can be used as inputs in this state. As inputs, Port 4 pins that are being pulled low externally will be a source of
current (IIL, on the datasheet) because of the internal pull-up transistor.
The secondary functions are assigned to the 5 pins of port 4 as follows:
P4.0: Regular Port I/O
P4.1: Regular Port I/O
P4.2/MISO:
Master Input Slave Output of SPI controller
P4.3/SCK:
Serial Clock of SPI controller
P4.4/MOSI:
Master Ouput Slave Input of SPI controller
It can drive CMOS inputs without external pull-ups.
IL
, see section "Electrical Characteristic") because of the internal pull-ups.
4383D–8051–02/08