LPC2294 Special Test Modes effecting JTAG and other operations
special test modes so far (edited for relevant info and to protect the
innocent), as we learn more I will be sure and post it here.
>>>> NXP E-mail chain <<<<
I had submitted a support request about two weeks ago dealing with loss
of JTAG communication with the LPC2294 part we are using. In the
response, Xxx had mentioned something about a test mode that the LPC
part enters if pin 22 (CAN TD1) is pulled low during reset. After some
investigation, we found that the TJA1040 CAN transceiver on channel one
was defective and forcing that line low.
In regards to this, what would cause the TxD line from a TJA1040 to be
pulled low internally? Also, can any details be given about this test
mode of the LPC2294 part? It appeared that the SPI communications from
the LPC2294 part were also failing when this test mode was invoked.
NXP Semiconductors answer:
I don't know of any normal condition that would cause the TXD line on
the TJA1040 to go low. If the 1040 wasn't powered up, there could be a
parasitic diode that would pull it low, but that is the only thing I can
think of other than a defective device.
And, unfortunately, the 2294 test mode details are proprietary.
Let us know if you need more info.
I have already inquired with our design team about the P1.22 "test mode"
and if there are others. Also, I have inquired if this same "test mode"
exists in the new /01 devices. I will forward more information as soon
as I receive it.
Field Applications Engineer
NXP Semiconductors - Founded by Philips
>>>> End NXP E-mail chain <<<<
Sr. Electronic Design Engineer
2604 Highway 20 North
Jamestown, ND 58401
From: l... [mailto:l...] On Behalf
Of Dave Such
Sent: Thursday, November 29, 2007 9:57 AM
Subject: Re: [lpc2000] Re: LPC2294JBD to LPC2294HBD difference
I too had this problem a while back. Faulty transceiver caused my JTAG
to not function. I didn't know why but replacing it restored the JTAG.
I too am interested in what this mode is.
Milender, Jeff wrote:
> Here is an FYI that I hope saves other the headache that we went
> We had lost the ability to communicate to our LPC2294 via JTAG and
> a couple weeks of trouble shooting traced it down to a failure of a
> transceiver that was holding TD1 low at power-up and otherwise
> correctly (as far as CAN communications was concerned). This caused
> LPC2294 to enter into a "Special Test Mode" that disables JTAG among
> other things.
> I have been unable to find any documentation on this "Special Test
> and only know about it through an e-mail from NXP that makes a
> to "Do not hold TD1 low while exiting reset. If TD1 is held low while
> exiting reset the LPC will enter a special test mode"
> If anyone has anymore information on this "Special Test Mode" I would
> love to see it, or any other "Special Test Modes" that are not
> documented in the LPC Data Sheet.
> Jeff Milender
> Sr. Electronic Design Engineer
> Cargo Systems
> Goodrich Interiors
> 2604 Highway 20 North
> Jamestown, ND 58401
> Tel: 701-253-7569
> From: l...
> Of Martin Maurer
> Sent: Wednesday, November 14, 2007 1:37 PM
> To: l...
> Subject: Re: [lpc2000] Re: LPC2294JBD to LPC2294HBD difference
> Hello Jeff,
> > >I have a product that was originally built using the LPC2294JBD144
> > > worked as expected.
> > > We are now receiving parts from our supplier that have the
> > > part and I have lost the ability to connect via JTAG.
> When the silicon is the same, an additional difference could be the
> bootloader version ?
> Just out of memory, how about protection dword (0x12345678), wasn't
> the ability to switch off JTAG ?