C517A_99 Datasheet, PDF (18/218 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

Introduction
C517A
Table 1-1
Pin Definitions and Functions (cont’d)
6\PERO
P4.0 - P4.7
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304)3 3/&&
64 - 66,
68 - 72
1 - 3,
5-9
PE/SWD
67
4
*) I = Input
O = Output
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I/O Port 4
is an 8-bit quasi-bidirectional I/O port with
internal pull-up resistors. Port 4 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
4 pins being externally pulled low will source
current (I _IL, in the DC characteristics)
because of the internal pull-up resistors.
Port 4 also serves as alternate compare
functions. 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 4 as follows :
P4.0 - P4.7 CM0 - CM7 Compare
channel 0 - 7
I
Power saving mode enable / Start
watchdog timer
A low level at this pin allows the software to
enter the power saving modes (idle mode,
slow down mode, and power down mode).
In case the low level is also seen during
reset, the watchdog timer function is off on
default.
Usage of the software controlled power
saving modes is blocked, when this pin is
held at high level. A high level during reset
performs an automatic start of the watchdog
timer immediately after reset.
When left unconnected this pin is pulled
high by a weak internal pull-up resistor.
During hardware power down the pullup
resisitor is switched off.
Semiconductor Group
1-12