Lpc2000

A client of mine who's been using the Nohau board for software
development zapped the JTAG inputs to the LPC2106 by connecting the
adaptor while the board was powered up - something to watch out for. I
replaced the LPC2106 with an LPC2104 (all I've got here) and got it
working again.

I suppose the safest thing to do is to power up the target board,
unplug the USB, connect the JTAG and plug it into the USB port on the PC.

Leon

Leon,

> --- In lpc2100@yahoogroups.com, "leon_heller" 
> <leon_heller@h...> wrote:
> > A client of mine who's been using the Nohau board for software 
> > development zapped the JTAG inputs to the LPC2106 by connecting the 
> > adaptor while the board was powered up - something to watch 
> out for. I 
> > replaced the LPC2106 with an LPC2104 (all I've got here) and got it 
> > working again.
> 
> 
> Apparently, the JTAG was connected with no power to the 
> board, which seems strange.

I probably have a static personality.  ;-)

--
Paul Curtis, Rowley Associates Ltd http://www.rowley.co.uk
CrossWorks for MSP430 and ARM processors

--- In lpc2100@yahoogroups.com, "leon_heller" <leon_heller@h...> wrote:
> A client of mine who's been using the Nohau board for software
> development zapped the JTAG inputs to the LPC2106 by connecting the
> adaptor while the board was powered up - something to watch out for. I
> replaced the LPC2106 with an LPC2104 (all I've got here) and got it
> working again.


Apparently, the JTAG was connected with no power to the board, which
seems strange.

Leon

As an aside, a client of mine does something similar to "safely" and
permanantly disable JTAG clock input on production units. This coupled
with replacing the boot loader makes device far more secure than what
CRP + Philips boot loader offers on other LPC parts. 

--- In lpc2000@yahoogroups.com, "leon_heller" <leon_heller@h...> wrote:
> A client of mine who's been using the Nohau board for software
> development zapped the JTAG inputs to the LPC2106 by connecting the
> adaptor while the board was powered up - something to watch out for. I
> replaced the LPC2106 with an LPC2104 (all I've got here) and got it
> working again.
> 
> I suppose the safest thing to do is to power up the target board,
> unplug the USB, connect the JTAG and plug it into the USB port on
the PC.

> 
> Leon
>

> As an aside, a client of mine does something similar to 
> "safely" and permanently disable JTAG clock input on 
> production units. 

Surely this has to be a risky procedure ?!  Zapping an input could
result in unpredictable current consumption, or even a part that runs
very hot and fails eventually. I imagine what you're doing is turning
one or more of the substrate protection diodes into carbon....

Cheers,
Bruce

This was my initial reaction.  I do not know the details but I am told
it involves multiple controlled energy discharges.  Apparently they do
this using jigs they already have for other purposes.  So I guess they
know what they are doing.

--- In lpc2000@yahoogroups.com, "Bruce Paterson" <bruce.paterson@b...>
wrote:

>
> > As an aside, a client of mine does something similar to 
> > "safely" and permanently disable JTAG clock input on 
> > production units. 
> 
> Surely this has to be a risky procedure ?!  Zapping an input could
> result in unpredictable current consumption, or even a part that runs
> very hot and fails eventually. I imagine what you're doing is turning
> one or more of the substrate protection diodes into carbon....
> 
> Cheers,
> Bruce

--- In lpc2000@yahoogroups.com, "leon_heller" <leon_heller@...> wrote:
>
> --- In lpc2100@yahoogroups.com, "leon_heller" <leon_heller@h...> wrote:
> > A client of mine who's been using the Nohau board for software
> > development zapped the JTAG inputs to the LPC2106 by connecting the
> > adaptor while the board was powered up - something to watch out for. I
> > replaced the LPC2106 with an LPC2104 (all I've got here) and got it
> > working again.
> 
> 
> Apparently, the JTAG was connected with no power to the board, which
> seems strange.

1. Your first message says that they zapped the chip by:
  a. Apply power to the LPC2106
  b. Connect the JTAG interface to the LPC2106

2. The second message indicates that they actually zapped the chip by:
  a. Cut power to the LPC2106
  b. Connect the JTAG interface to the LPC2106

Which case was it really? What JTAG interface circuit were they using?
Were they using a wiggler clone?

In case 1, I don't understand why this would zap the chip. 

Case 2 makes more sense to me. If the LPC2106 Vdd power supply is not
powered, and you apply some 3V logic voltages to the JTAG pins, you're
probably violating the chip's absolute maximum ratings. Most CMOS
chips say input pins are not allowed to be driven higher than the
power supply voltage, plus maybe a small extra amount (0.5VDC in the
case of LPC2106). If Vdd is at 0VDC, then applying more than 0.5VDC to
input pins will be exceeding the absolute maximum ratings.

This is also a potential problem with the 74AC244 wiggler clones. If
the 74AC244 is running off the target board's 3.3VDC, then we
shouldn't drive the 74AC244 inputs beyond 3.3 + 0.5 = 3.8VDC according
to the 74AC244 datasheet. However, the parallel port side of the
wiggler clone is driven by 5V, doh! Maybe this could contribute to
wiggler clones acting flakey?

At least by powering the 74AC244 from the target's 3.3VDC, the wiggler
clones should protect the LPC2106 from dying in Case 2 because the
JTAG input pins will only be driven by the wiggler clone if the
LPC2106 is already powered up (and thus powering the 74AC244). 

VHC logic chips are special in that they do not have the restriction
that input pins can not exceed the power supply voltage level. That is
why I think the parallel port JTAG debuggers should be using a
74VHC chip to convert from 5V logic to 3V logic. The 74VHC can be
powered at 3V while still accepting 5V at it's inputs without over
stressing the part.

--
K9spud Microcontroller Electronics
http://www.k9spud.com/

----- Original Message ----- 

From: "Ed Schlunder" <zilym@...>
To: <lpc2000@yahoogroups.com>
Sent: Friday, February 03, 2006 7:41 AM
Subject: [lpc2000] Re: JTAG warning


> --- In lpc2000@yahoogroups.com, "leon_heller" <leon_heller@...> wrote:
>>
>> --- In lpc2100@yahoogroups.com, "leon_heller" <leon_heller@h...> wrote:
>> > A client of mine who's been using the Nohau board for software
>> > development zapped the JTAG inputs to the LPC2106 by connecting the
>> > adaptor while the board was powered up - something to watch out for. I
>> > replaced the LPC2106 with an LPC2104 (all I've got here) and got it
>> > working again.
>>
>>
>> Apparently, the JTAG was connected with no power to the board, which
>> seems strange.
>
> 1. Your first message says that they zapped the chip by:
>  a. Apply power to the LPC2106
>  b. Connect the JTAG interface to the LPC2106
>
> 2. The second message indicates that they actually zapped the chip by:
>  a. Cut power to the LPC2106
>  b. Connect the JTAG interface to the LPC2106
>
> Which case was it really? What JTAG interface circuit were they using?
> Were they using a wiggler clone?
>
> In case 1, I don't understand why this would zap the chip.
>
> Case 2 makes more sense to me. If the LPC2106 Vdd power supply is not
> powered, and you apply some 3V logic voltages to the JTAG pins, you're
> probably violating the chip's absolute maximum ratings. Most CMOS
> chips say input pins are not allowed to be driven higher than the
> power supply voltage, plus maybe a small extra amount (0.5VDC in the
> case of LPC2106). If Vdd is at 0VDC, then applying more than 0.5VDC to
> input pins will be exceeding the absolute maximum ratings.
>
> This is also a potential problem with the 74AC244 wiggler clones. If
> the 74AC244 is running off the target board's 3.3VDC, then we
> shouldn't drive the 74AC244 inputs beyond 3.3 + 0.5 = 3.8VDC according
> to the 74AC244 datasheet. However, the parallel port side of the
> wiggler clone is driven by 5V, doh! Maybe this could contribute to
> wiggler clones acting flakey?
>
> At least by powering the 74AC244 from the target's 3.3VDC, the wiggler
> clones should protect the LPC2106 from dying in Case 2 because the
> JTAG input pins will only be driven by the wiggler clone if the
> LPC2106 is already powered up (and thus powering the 74AC244).
>
> VHC logic chips are special in that they do not have the restriction
> that input pins can not exceed the power supply voltage level. That is
> why I think the parallel port JTAG debuggers should be using a
> 74VHC chip to convert from 5V logic to 3V logic. The 74VHC can be
> powered at 3V while still accepting 5V at it's inputs without over
> stressing the part.

That was a long time ago, and they weren't all that sure what they did. I 
can't even remember what JTAG interface they were using. I thought the 
parallel port uses TTL signals - VIH is 3.3 V max.

Leon