Important changes to forums and questions
All forums and questions are now archived. To start a new conversation or read the latest updates go to forums.mbed.com.
11 years, 7 months ago.
JTAG signals needed to program target and purpose of TGT_SBL_ISP and TGT_JTAG_IRQ
Hello,
I'm wondering what signals are actually necessary to perform the JTAG programming between the "magic" IC and the target (LPC11U24). The idea is to remove the target chip and replace with a JTAG header, allowing the mbed to program LPC11U24s on other boards using an existing JTAG interface. For the moment, we are using LPCXpresso for this, but prefer the mbed design model. I do know that it is possible to program mbed-generated binaries by other means, but the idea is to eliminate the need for any other software/hardware.
I believe it should be possible to program a target by bringing out only the TGT_NRESET_TO_IC, TGT_SWCLK, and TGT_SWDIO. This is because other articles on the forums suggest programming the target is done using only the JTAG interface (not ISP).
However, the mbed schematic shows two other signals connected between the magic IC and the target: TGT_SBL_ISP and TGT_JTAG_IRQ. The first, if driven low during reset, could be used to enter ISP mode. I don't know what the second does. The IRQ is particularly unusual in that it seems to be connected to a standard IO pin with no additional functionality mentioned in the LPC11U24's datasheet. The existence of the ISP pin makes me worry that without connecting this and UART, the process will fail.
So what do these signals do and are they needed? Are there any other gotchas or should I be ok to connect only the three standard JTAG signals I mentioned earlier (reset, clk, and io)?
Cheers, Carl
1 Answer
11 years, 6 months ago.
You can keep the mbed for prototyping , and have " mbed pinout " boards with JTAG but no magic chip for the production boards There is a very nice LPC11U24 mini pcb design by Thanasis Mavrogeorgiadis
have you seen it ?
http://mbed.org/forum/electronics/topic/4059/
Cheers , Christos
Hi Christos,
Thanks for this. It's interesting but not quite what we had in mind. We already have prototype boards containing LPC11U24s programmable by JTAG using a header. The idea was to bring out the pins from the magic chip on the mbed to a header so that we could program these existing boards. The mbed would become a portable programmer. These boards do not have USB or UART brought out, so using ISP is not an option. At the moment we use LPCxpresso, but this requires software and drivers to be installed.
In any case, we've decided to go another way. I'd still be interested in knowing what those pins do if anyone knows, however.
Cheers, Carl
posted by 19 Nov 2012