SAB80C517 Datasheet, PDF (9/61 Pages) Siemens Semiconductor Group – 8-Bit CMOS Single-Chip Microcontroller

SAB 80C517/80C537
Pin Definitions and Functions (cont’d)
Symbol
Pin Number
I/O ^*) _Function
P-LCC-84 P-MQFP-100-2
P3.0 - P3.7 21 - 28
90 - 97
* _{I = Input}
O = Output
I/O Port 3
is a bidirectional I/O port with internal
pull-up resistors. Port 3 pins that have
1 s written to them are pulled high by
the internal pull-up 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
pull-up resistors. Port 3 also contains
the interrupt, timer, serial port 0 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 × D0 (P3.0): receiver data input
(asynchronous) or data input/output
(synchronous) of serial interface
– T × D0 (P3.1): transmitter data
output (asynchronous) or clock
output (synchronous) of serial
interface 0
– INT0 (P3.2): interrupt 0 input/timer 0
gate control
– INT1 (P3.3): interrupt 1 input/timer 1
gate control
– 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
Semiconductor Group
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