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Fig 13. Push-pull output.
5.6 Port 0 and Analog Comparator functions
The P89LPC938 incorporates two Analog Comparators. In order to give the best analog
performance and minimize power consumption, pins that are being used for analog
functions must have both the digital outputs and digital inputs disabled.
Digital outputs are disabled by putting the port pins into the input-only mode as described
in the Port Configurations section (see
Digital inputs on Port 0 may be disabled through the use of the PT0AD register. Bits 1
through 5 in this register correspond to pins P0.1 through P0.5 of Port 0, respectively.
Setting the corresponding bit in PT0AD disables that pin's digital input. Port bits that have
their digital inputs disabled will be read as 0 by any instruction that accesses the port.
On any reset, PT0AD bits 1 through 5 default to logic 0s to enable the digital functions.
5.7 Additional port features
After power-up, all pins are in Input-Only mode. Please note that this is different from
the LPC76x series of devices.
Every output on the P89LPC938 has been designed to sink typical LED drive current.
However, there is a maximum total output current for all ports which must not be
exceeded. Please refer to the P89LPC938 data sheet for detailed specifications.
All ports pins that can function as an output have slew rate controlled outputs to limit noise
generated by quickly switching output signals. The slew rate is factory-set to
approximately 10 ns rise and fall times.
User manual
port latch
•
After power-up, all I/O pins except P1.5, may be configured by software.
•
Pin P1.5 is input only. Pins P1.2 and P1.3 are configurable for either input-only or
open drain.
Rev. 03 — 7 June 2005
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Figure
12).
UM10119
P89LPC938 User manual
port
pin
glitch rejection
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© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
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