Introduction
C513AO
User’s Manual
1-8
05.99
P3.0-
P3.7
10-17
10
11
12
13
14
15
16
17
11,
13-19
11
13
14
15
16
17
18
19
5,
7-13
5
7
8
9
10
11
12
13
I/O Port 3
Port 3 is an 8-bit quasi-bidirectional port with internal pull-
up arrangement. Port 3 pins that have “1”s written to them
are pulled high by the internal pull-up transistors and in
that state can be used as inputs. As inputs, Port 3 pins
being externally pulled low will source current (
I
IL
, in the
DC characteristics) because of the internal pull-up
transistors.
The output latch corresponding to a secondary function
must be programmed to a “1” 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 (asynch.) or data
input/output (synch.) of serial
interface
P3.1 / TxD
Transmitter data output (asynch.) or
clock output (synch.) of 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
WR control output; latches the data
byte from Port 0 into the external data
memory
P3.7 / RD
RD control output; enables the
external data memory to Port 0
*)
I = Input
O = Output
Table 1-1
Pin Definitions and Functions (cont’d)
Symbol Pin Number
I/O
*)
Function
P-DIP-40
P-LCC-
4
4
P-MQ
F
P-44
