Lpc2000

Doesn't look like a software problem at all. The Keil board has the 
usual arrangement of transistors joining RTS to /RST and DTR to P0.14. 
With the jumpers removed to disconnect the transistors from /RST and 
P0.14, all works fine.

And even when I use my RS232 breakout box to disconnect DTR and RTS from 
the host, during high activity on the RS232 TD or RD lines, the outputs 
of the two transistors for /RST and P0.14 show noise at about 10KHz 
(unsurprising from 9600 baud comms) of about 2v (in the case of the 
P0.14 line, with a 22K pullup) and 1v (in the case of /RST, with a 10K 
pullup).

Alas, I can't too easily get scope probes onto the gates of the 
transistors on the board because they're tiny surface mount ones, but 
I'll try investigating those next to see what's happening there. 
Interestingly, with RTS and DTR disconnected from the host, a scope put 
on thise lines at my breakout box is showing noise similar to the noise 
on the outputs of the transistors - so I suspect the noise is coming 
into the lines on the gate circuit somewhere.

Now, the schematic for my MCB2100 board shows pretty much the exact same 
circuit as listed under RTS_DTR.DOC in the files section. I doubt it's 
an actual circuit problem, since there's no electrical connection 
between the DTR/RTS stuff and the RD/TD stuff, so I guess it's probably 
a problem with the layout of the board or something - but if anyone else 
has a board that does the DTR/RTS thing, could they possibly try maxing 
out the RS232 port while watching the actual /RST and P0.14 lines with a 
scope, to see what they can find?

Anyway, with the jumpers pulled on the board so the lines on the CPU are 
only connected to the pushbuttons, it works fine :-)

I'm planning on building a board with an RS232 transceiver and DTR/RTS 
ISP logic (to meet the fine new Standard ISP Header spec that Rickman 
has been helping with on the Wiki!) - I think I'll build it on 
breadboard first and experiment to make sure it doesn't end up 
exhibiting the same problem.

Thanks,

ABS

At 03:27 PM 2/28/04 +0000, you wrote:

>Now, the schematic for my MCB2100 board shows pretty much the exact same
>circuit as listed under RTS_DTR.DOC in the files section. I doubt it's
>an actual circuit problem, since there's no electrical connection
>between the DTR/RTS stuff and the RD/TD stuff, so I guess it's probably
>a problem with the layout of the board or something - but if anyone else
>has a board that does the DTR/RTS thing, could they possibly try maxing
>out the RS232 port while watching the actual /RST and P0.14 lines with a
>scope, to see what they can find?

I should have a couple of boards coming in a few days.  I'll take a look.

Robert

" 'Freedom' has no meaning of itself.  There are always restrictions,
be they legal, genetic, or physical.  If you don't believe me, try to
chew a radio signal. "

                         Kelvin Throop, III

At 05:57 PM 2/28/04 -0500, you wrote:
>At 03:27 PM 2/28/04 +0000, you wrote:
>
> >Now, the schematic for my MCB2100 board shows pretty much the exact same
> >circuit as listed under RTS_DTR.DOC in the files section. I doubt it's
> >an actual circuit problem, since there's no electrical connection
> >between the DTR/RTS stuff and the RD/TD stuff, so I guess it's probably
> >a problem with the layout of the board or something - but if anyone else
> >has a board that does the DTR/RTS thing, could they possibly try maxing
> >out the RS232 port while watching the actual /RST and P0.14 lines with a
> >scope, to see what they can find?
>
>I should have a couple of boards coming in a few days.  I'll take a look.

I've had a chance to do some preliminary testing.  Other than an extra 
inversion on some pins and some mechanical fit issues I've had no 
problems.  I'm using FETs rather than transistors but I've seen only a 
little noise (~20mV with 60mV spikes at a 1.25MHz period) on the gates 
presumably from the level translators switching supply.

I've still got some testing to do, different speeds etc.., and I want to 
replace the patched in through hole caps with proper smt ones but it looks 
like it will be fine.

Robert

" 'Freedom' has no meaning of itself.  There are always restrictions,
be they legal, genetic, or physical.  If you don't believe me, try to
chew a radio signal. "

                         Kelvin Throop, III