LPC MicrocontrollersのトピックJTAG/SWD interface connection on LPC1778

JTAG/SWD interface connection on LPC1778

lpcware — Wed, 15 Jun 2016 17:48:36 GMT

Content originally posted in LPCWare by giusloq on Wed Apr 13 00:59:39 MST 2016
Two questions related to JTAG/SWD interface on LPC1778 device.

The User Manual (Figure 176 on page 909) shows the connection of Cortex Debug connector. The pin 10 is connected to nRESET, the general reset input of MCU. Is it correct? Should I connect pin 10 to JTAG_TRST? Is it the same?

Second question. User Manual shows a pull-up resistor on JTAG_TDO pin. It's an output from the MCU, why a pull-up should be used?

Re: JTAG/SWD interface connection on LPC1778

lpcware — Wed, 15 Jun 2016 17:48:37 GMT

Content originally posted in LPCWare by vtw.433e on Wed Apr 13 01:06:37 MST 2016
See this FAQ
https://www.lpcware.com/content/faq/lpcxpresso/debug-design

Re: JTAG/SWD interface connection on LPC1778

lpcware — Wed, 15 Jun 2016 17:48:39 GMT

Content originally posted in LPCWare by giusloq on Thu Apr 14 04:06:54 MST 2016
From https://www.lpcware.com/content/faq/lpcxpresso/debug-design

Quote:
Note for TCK/SWCLK, although a pull-down is recommended, you can alternatively use a pull-up. The main thing is that it does not float. Note in particular that if the MCU provides an internal pull-up on this signal, then adding an external pull-down on the board is not recommended.

Quote:
Some MCUs do not include internal pull-up or pull-down resistors on JTAG/SWD pins. You will need to review the datasheet for the specific MCU being used to confirm.

UM10470 for LPC178x/177x says JTAG_TMS and JTAG_TDI pins have an internal pull-up. So the board should provide external pull-up on JTAG_TCK and JTAG_TDO (as indicated in the figure 176 on page 909).
However the link above suggest to use a pull-down on JTAG_TCK, but UM10470 shows a pull-up...

UM10360 for LPC176x/175x doesn't say anything about internal pull-up. Does this mean I should add 4 external pull-up resistors on all JTAG pins?

Re: JTAG/SWD interface connection on LPC1778

lpcware — Wed, 15 Jun 2016 17:48:39 GMT

Content originally posted in LPCWare by mostafanfs on Thu Apr 14 22:57:50 MST 2016
It'a all clear in this page :
https://www.lpcware.com/content/faq/lpcxpresso/debug-design

Yes. you could use pull up resistors for JTAG pins except TCK which is better to pull it down with 10K

Re: JTAG/SWD interface connection on LPC1778

lpcware — Wed, 15 Jun 2016 17:48:40 GMT

Content originally posted in LPCWare by giusloq on Fri Apr 15 00:14:48 MST 2016

Quote:
It'a all clear in this page :
https://www.lpcware.com/content/faq/lpcxpresso/debug-design

What is not clear to me is the internal pull-up/down resistors for LPC1769. The datasheet says nothing about them. Does this mean they are absent?

It's strange, because big brothers LPC1778 does have internal pull-ups on some JTAG pins.

Re: JTAG/SWD interface connection on LPC1778

lpcware — Wed, 15 Jun 2016 17:48:41 GMT

Content originally posted in LPCWare by mostafanfs on Fri Apr 15 02:10:51 MST 2016
Dont know about Datasheet but I've seen JTAGs worked with or even without Pull-up resistor for LPC1768 so why dont you just put them to stop worrying about the whole thing ?

Re: JTAG/SWD interface connection on LPC1778

lpcware — Sun, 19 Jun 2016 01:08:03 GMT

bump