C541U Datasheet, PDF (8/63 Pages) Siemens Semiconductor Group – 8 BIT CMOS MICROCONTROLLER

C541U
Table 1
Pin Definitions and Functions (cont’d)
Symbol
Pin I/O*) Function
Numbers
P-LCC-44
P3.0 - P3.7 11, 13 - 19 I/O
11
13
14
15
16
17
18
19
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 pin with LED drive capability are able to sink
current up to 10 mA. 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 / LED2 LED2 output
P3.1 / DADD Device attached input
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
XTAL2
20
– XTAL2
is the output of the inverting oscillator amplifier. This pin is used
for the oscillator operation with crystal or ceramic resonator.
XTAL1
21
– XTAL1
is the input to the inverting oscillator amplifier and input to the
internal clock generator circuits.
To drive the device from an external clock source, XTAL1 should
be driven, while XTAL2 is left unconnected. Minimum and
maximum high and low times as well as rise/fall times specified in
the AC characteristics must be observed.
*) I = Input
O = Output
Semiconductor Group
6