C517A_99 Datasheet, PDF (19/218 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

Introduction
C517A
Table 1-1
Pin Definitions and Functions (cont’d)
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P3.0 - P3.7
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90 - 97
21 - 28
90
21
91
22
92
23
93
24
94
25
95
26
96
27
97
28
*) I = Input
O = Output
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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 / RxD0 Receiver data input
(asynch.) or data
input/output (synch.)of
serial interface 0
P3.1 / TxD0 Transmitter data output
(asynch.) or clock output
(synch.) of serial interface
0
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
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