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Pin Definitions and Functions (cont'd)
Symbol
Pin
P-LCC-68
P3.0-P3.7 21-28
Semiconductor Group
Pin
Input (I)
P-MQFP-80
Output (O)
15-22
I/O
Function
Port 3
is an 8-bit bidirectional I/O port with
internal pullup resistors. Port 3 pins that
have1's written to them are pulled high by
the internal pullup resistors, and in that
state can be used as inputs. As inputs,
port 3 pins being externally pulled low will
source current (I
characteristics) because of the internal
pullup resistors. Port 3 also contains the
interrupt, timer, serial port and external
memory strobe pins that are used by
various options. The output latch
corresponding to a secondary function
must be programmed to a one (1) for that
function to operate. The secondary
functions are assigned to the pins of port
*
3, as follows:
×
– R
D (P3.0): serial port's receiver data
input (asynchronous) or data input/
output (synchronous)
×
– T
D (P3.1): serial port's transmitter data
output
(asynchronous) or clock output
(synchronous)
– INT0 (P3.2): interrupt 0 input/timer 0
gate control input
– INT1 (P3.3): interrupt 1 input/timer 1
gate control input
– T0 (P3.4): counter 0 input
– T1 (P3.5): counter 1 input
– WR (P3.6): the write control signal
latches the data byte from port 0 into the
external data memory
– RD (P3.7): the read control signal
enables the external data memory to
port 0
221
Device Specifications
, in the DC
IL
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