High-Performance SAB 80C517A/83C517A-5 8-Bit CMOS Single ...

SAB 80C517A/83C517A-5Pin Definitions and Functions (cont’d)Symbol Pin Number I/O *) FunctionP-LCC-84P-MQFP-100-2P3.0 - P3.7 21 - 28 90 - 97 I/O Port 3is a bidirectional I/O port with internal pullupresistors. Port 3 pins that have 1 swritten to them are pulled high by theinternal pull-up resistors, and in that statecan be used as inputs. As inputs, port 3pins being externally pulled low will sourcecurrent (I IL, in the DC characteristics)because of the internal pull-up resistors.Port 3 also contains the interrupt, timer,serial port 0 and external memory strobepins that are used by various options. Theoutput latch corresponding to a secondaryfunction must be programmed to a one (1)for that function to operate.The secondary functions are assigned tothe pins of port 3, as follows:– R × D0 (P3.0): receiver data input(asynchronous) or data input/output(synchronous) of serial interface– T × D0 (P3.1): transmitter data output(asynchronous) or clock output(synchronous) of serial interface 0– INT0 (P3.2): interrupt 0 input/timer 0gate control– INT1 (P3.3): interrupt 1 input/timer 1gate control– T0 (P3.4): counter 0 input– T1 (P3.5): counter 1 input– WR (P3.6): the write control signallatches the data byte from port 0 into theexternal data memory– RD (P3.7): the read control signalenables the external data memory toport 0* I = InputO = OutputSemiconductor Group 9