Any restrictions for Pin 33, 34 or 35 ?

Any restrictions for Pin 33, 34 or 35 ?

Postby Borje » Mon Jan 20, 2014 6:13 am

Hi
I get a strange behavior when I connect pin 33 to a ULN2003 driver input. The autostart led stops flash on powerup and the yellow led lights up steady, the RTC resets and the connection to PC fails. The nominal load on pin is 2.7 Kohm from ULN2003
Other pins 29-32 work fine when connected to ULN 2003
I cant find any restrictions for use of pin 33-35 in the manual.
Last edited by Borje on Tue Jan 21, 2014 4:40 am, edited 1 time in total.
Borje
 
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Re: Any restrictions for Pin 33, 34 or 35 ?

Postby Daniel » Mon Jan 20, 2014 11:03 am

Hi Borje

I'm not aware of any but it doesn't mean there aren't any. The LPC2136 User Manual is 300 pages and then there's another 50 pages or so in the datasheet and somewhere in there there may be a restriction on pulling pins high or low during power on.

I don't quite understand which pin has the issue since you seem to have a typo in the message.

After reading the datasheet I found this for pin 34 on the EzSBC1 (p1.20) "TRACESYNC — Trace Synchronization. Standard I/O port with internal pull-up. LOW on TRACESYNC while RESET is LOW enables pins P1.25:16 to operate as Trace port after reset."

I disable the TRACE port in the programming of the part (and the JTAG port) so I thought the function is off and doesn't affect the part. I don't understand why the part would hang if it finds this pin low on reset. I will figure out what is happening and amend the manual, if necessary.

Daniel
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Re: Any restrictions for Pin 33, 34 or 35 ?

Postby Borje » Mon Jan 20, 2014 12:48 pm

Thanks Daniel
We decided to not use pin 33,34,35, they are now floating, I changed the layout on my prototype to avoid them so there is no issue for me any longer. It seems to be pin 33 or 34 that give problems on power up , but I don't have time to dig in to it

Note: My Basic program do not hang, it starts up as it should, but the LED function is strange and the connection to PC is lost.

Best regards
Borje
Borje
 
Posts: 10
Joined: Sat Nov 09, 2013 6:39 am


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