Hi Nick, something similar happens in LPC2292.
Although user manual says "All Port 1 pins are 5V tolerant with built-in
pull-up resistor that sets input level to high when corresponding pin is
used as input", I found this not to be the case because of "external boot"
feature provided by the boot loader that is mentioned elsewhere as BOOT1:0
signals.
What this "feature" does is configures external memory to 8/16/32 bit mode
depending on P2.26 and P2.27 at reset. When this happens, some pins of P1
assume external memory interface functions and thus become outputs. The
code implementing this feature in LPC2292 boot loader V 1.64 appears strange.
Try making sure that P2.26-27 are not connected (and depend on internal
pull-up) to see if you still get this behaviour. If you have things
connected to these pins, the other option active pull-up during reset.
Hope this helps.
Jaya
>Message: 6
> Date: Mon, 06 Mar 2006 05:44:25 -0000
> From: "nknight62" <justlooking@...>
>Subject: LPC2138 GPIO Pull Downs ?
>
>We have an application where we use the GPIO I/O pins on Port 1 of
>LPC2138 to an LCV244 buffer/driver. We found that randomly, some pins
>on the buffer driver were high or low at power-up with no program
>loaded to control the pins. We added 32k pull downs between the 2138
>and the buffer/driver inputs to pull the lines low because the GPIO
>lines are floating inputs before program changes them into outputs.
>However, we are still randomly seeing some outputs on buffer/driver
>high and some low on power up. We measured between 0.4 and 1.2 volts
>on those lines. Why are 32k pull downs not working for us ?
>
>Regards,
>Nick
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