C515A Datasheet, PDF (8/58 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

C515A
Table 1
Pin Definitions and Functions (cont’d)
Symbol
P3.0-P3.7
*) I = Input
O = Output
Pin Number
(P-MQFP-80)
15-22
15
16
17
18
19
20
21
22
I/O*)
I/O
Function
Port 3
is an 8-bit quasi-bidirectional I/O port with internal pullup
resistors. Port 3 pins that have 1'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 _IL, in the DC
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:
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
Semiconductor Group
8
1997-10-01