C515C Datasheet, PDF (8/69 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

C515C
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*) Function
I/O 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
1997-07-01