LPC2138 UART1 problem

Started by wirelessisgood June 27, 2006
Has anyone come across this problem?

UART0 and UART1 are set up identically. 115Kbaud, 8,N,1. No modem
features.
Both works, but after about 1 hour, UART1 stops receiving. UART1 still
transmits properly.

Resetting IC does not get UART1 to work again.
Power Cycling does not get UART1 to work again.
Replacing the IC, however, does get UART1 to work again, but only for
a brief time. Then UART1 stops receiving. UART0 hums along just fine.

Each UART is connected to a MAX3072E part, in identical circuits. We
have replaced components all around the LPC2138 as well and checked
all voltages and all seem to be in the good range.

Using the IAR debugger to see what's happening after the failure, we
get a UART1 modem interrupt after reset (while interrupts are
disabled) and no other UART1 interrupts after all interrupts are
cleared.

Any suggestions?

Thanks!

Mike

An Engineer's Guide to the LPC2100 Series

When you say you have power-cycled the board does that mean you simply
disconnected the power or did you disconnect everything that may be
leaking current into the circuit? A good short across the 3.3V supply
after power-down should convince it.

Have you scoped the Rxd pin on the cpu to make sure it is getting the
data? (probably does)

Does sound very much like software though, care to enlighten us a bit more?

*Peter*

wirelessisgood wrote:
> Has anyone come across this problem?
>
> UART0 and UART1 are set up identically. 115Kbaud, 8,N,1. No modem
> features.
> Both works, but after about 1 hour, UART1 stops receiving. UART1 still
> transmits properly.
>
> Resetting IC does not get UART1 to work again.
> Power Cycling does not get UART1 to work again.
> Replacing the IC, however, does get UART1 to work again, but only for
> a brief time. Then UART1 stops receiving. UART0 hums along just fine.
>
> Each UART is connected to a MAX3072E part, in identical circuits. We
> have replaced components all around the LPC2138 as well and checked
> all voltages and all seem to be in the good range.
>
> Using the IAR debugger to see what's happening after the failure, we
> get a UART1 modem interrupt after reset (while interrupts are
> disabled) and no other UART1 interrupts after all interrupts are
> cleared.
>
> Any suggestions?
>
> Thanks!
>
> Mike

This may sound stupid, but if the board is a new design, use a scope to
confirm the voltage levels of the signal going to the RX pin are within
spec. Possibly the MAX3072E is wired up incorrectly or something else
is pulling the line too high or low.

Regards
-Bill Knight

Peter Jakacki wrote:
> When you say you have power-cycled the board does that mean you simply
> disconnected the power or did you disconnect everything that may be
> leaking current into the circuit? A good short across the 3.3V supply
> after power-down should convince it.
>
> Have you scoped the Rxd pin on the cpu to make sure it is getting the
> data? (probably does)
>
> Does sound very much like software though, care to enlighten us a bit more?
>
> *Peter*
>
> wirelessisgood wrote:
>>
>> Has anyone come across this problem?
>>
>> UART0 and UART1 are set up identically. 115Kbaud, 8,N,1. No modem
>> features.
>> Both works, but after about 1 hour, UART1 stops receiving. UART1 still
>> transmits properly.
>>
>> Resetting IC does not get UART1 to work again.
>> Power Cycling does not get UART1 to work again.
>> Replacing the IC, however, does get UART1 to work again, but only for
>> a brief time. Then UART1 stops receiving. UART0 hums along just fine.
>>
>> Each UART is connected to a MAX3072E part, in identical circuits. We
>> have replaced components all around the LPC2138 as well and checked
>> all voltages and all seem to be in the good range.
>>
>> Using the IAR debugger to see what's happening after the failure, we
>> get a UART1 modem interrupt after reset (while interrupts are
>> disabled) and no other UART1 interrupts after all interrupts are
>> cleared.
>>
>> Any suggestions?
>>
>> Thanks!
>>
>> Mike
Bill Knight wrote:

> This may sound stupid, but if the board is a new design, use a scope to
> confirm the voltage levels of the signal going to the RX pin are within
> spec. Possibly the MAX3072E is wired up incorrectly or something else
> is pulling the line too high or low.
>
Yeah, it would be possible for the RX circuit to work if wired backward,
until it hammered the pin to death. IOW, a driver is wired as use as a
receiver. The input to the driver would see RS232C as valid TTL / CMOS
levels while the output of the driver could be hammering the LPC2138
UART RX with +/- 5 volts. The RX input of the LPC2138 is 5volt
tolerant, so banging below 0volts may take a while to kill it.

You probably would not see anything obviously wrong on a scope though.

TomW

--
Tom Walsh - WN3L - Embedded Systems Consultant
http://openhardware.net, http://cyberiansoftware.com
"Windows? No thanks, I have work to do..."
----------------

--- In l..., Peter Jakacki wrote:
>
> When you say you have power-cycled the board does that mean you
simply
> disconnected the power or did you disconnect everything that may
be
> leaking current into the circuit? A good short across the 3.3V
supply
> after power-down should convince it.
>
> Have you scoped the Rxd pin on the cpu to make sure it is getting
the
> data? (probably does)
>
> Does sound very much like software though, care to enlighten us a
bit more?
>
> *Peter*
>
> wirelessisgood wrote:
> >
> >
> > Has anyone come across this problem?
> >
> > UART0 and UART1 are set up identically. 115Kbaud, 8,N,1. No modem
> > features.
> > Both works, but after about 1 hour, UART1 stops receiving. UART1
still
> > transmits properly.
> >
> > Resetting IC does not get UART1 to work again.
> > Power Cycling does not get UART1 to work again.
> > Replacing the IC, however, does get UART1 to work again, but
only for
> > a brief time. Then UART1 stops receiving. UART0 hums along just
fine.
> >
> > Each UART is connected to a MAX3072E part, in identical
circuits. We
> > have replaced components all around the LPC2138 as well and
checked
> > all voltages and all seem to be in the good range.
> >
> > Using the IAR debugger to see what's happening after the
failure, we
> > get a UART1 modem interrupt after reset (while interrupts are
> > disabled) and no other UART1 interrupts after all interrupts are
> > cleared.
> >
> > Any suggestions?
> >
> > Thanks!
> >
> > Mike
>

Posted a reply earlier but for some reason it didn't turn out.

Thanks to all for your insights.

We have never had this problem on boards that have worked for
weeks/months (and still working). We suspect that we got a bad lot
of parts when we built additional boards. The suspect parts have
date codes 0551B and 0552B. We replaced the parts with different
date codes and so far things are running smoothly again and now are
in regression tests.

It seems that this problem has not happened to anyone in this forum
so it gives us more confidence that it's lot-related.

Thanks again for all your help.

Mike

--- In l..., "wirelessisgood"
wrote:
>
> --- In l..., Peter Jakacki wrote:
> >
> > When you say you have power-cycled the board does that mean you
> simply
> > disconnected the power or did you disconnect everything that may
> be
> > leaking current into the circuit? A good short across the 3.3V
> supply
> > after power-down should convince it.
> >
> > Have you scoped the Rxd pin on the cpu to make sure it is
getting
> the
> > data? (probably does)
> >
> > Does sound very much like software though, care to enlighten us
a
> bit more?
> >
> > *Peter*
> >
> > wirelessisgood wrote:
> > >
> > >
> > > Has anyone come across this problem?
> > >
> > > UART0 and UART1 are set up identically. 115Kbaud, 8,N,1. No
modem
> > > features.
> > > Both works, but after about 1 hour, UART1 stops receiving.
UART1
> still
> > > transmits properly.
> > >
> > > Resetting IC does not get UART1 to work again.
> > > Power Cycling does not get UART1 to work again.
> > > Replacing the IC, however, does get UART1 to work again, but
> only for
> > > a brief time. Then UART1 stops receiving. UART0 hums along
just
> fine.
> > >
> > > Each UART is connected to a MAX3072E part, in identical
> circuits. We
> > > have replaced components all around the LPC2138 as well and
> checked
> > > all voltages and all seem to be in the good range.
> > >
> > > Using the IAR debugger to see what's happening after the
> failure, we
> > > get a UART1 modem interrupt after reset (while interrupts are
> > > disabled) and no other UART1 interrupts after all interrupts
are
> > > cleared.
> > >
> > > Any suggestions?
> > >
> > > Thanks!
> > >
> > > Mike
>