Rainbow Electronics T89C51CC01 - Manual (Page 6)

6
T89C51CC01
Rev. D – 17-Dec-01
P3.0:7 I/O
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
IL
, see section "Electrical Characteristic") because of the internal pull-ups.
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:
Timer 1 counter input
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.
P4.0:1 I/O
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 output latch corresponding to a secondary function RxDC must be programmed to one for that function to operate. The
secondary functions are assigned to the two pins of port 4 as follows:
P4.0 / TxDC:
Transmitter output of CAN controller
P4.1 / RxDC:
Receiver input of CAN controller.
It can drive CMOS inputs without external pull-ups.
Pin Name Type Description