Re: Use of TRST on ST vs. Luminary ARM JTAG?

On 11/02/2012 06:10, Tim Wescott wrote:
I'm using an ST ARM Cortex part for the first time. I've been using
Luminary parts until now.

I notice that on the Olimex demo board for the STM32F103RBT6, they have
the JTAG TRST pin connected, but on the Luminary eval board for the
LM3S811 the TRST pin is left open.

Does anyone know why this is? Is it just that the TRST pin is sorta
optional, and the Luminary folks weren't in a mood to dot all their 'i's
and cross all their 't's? Is there some reason that you might _not_ want
to connect TRST?

I also see that the Olimex board has a solderable bridge to connect TRST
to the processor reset. Again -- why, do you know the advantages and
disadvantages?

I'm going to just copy the Olimex board, but I'm curious as to just what
it is that I am so blindly doing...

The Keil Ulink interface supports JTAG and the ARM SW debug interface. SW uses fewer pins and works at least as well. Keil suggest connecting the reset pin which can be used to reset the processor from the debugger. If the software (on the target) sets the target clock to something useless (like off or too fast or very slow) JTAG won't work any more so being able to reset from the debug port is very useful.

Michael Kellett
.

Relevant Pages

  • Use of TRST on ST vs. Luminary ARM JTAG?
    ... LM3S811 the TRST pin is left open. ... I also see that the Olimex board has a solderable bridge to connect TRST ... My liberal friends think I'm a conservative kook. ...
    (comp.arch.embedded)
  • Re: Use of TRST on ST vs. Luminary ARM JTAG?
    ... I notice that on the Olimex demo board for the STM32F103RBT6, ... the JTAG TRST pin connected, ... LM3S811 the TRST pin is left open. ... Processor reset is usually tied to high capacitive ...
    (comp.arch.embedded)
  • Re: Use of TRST on ST vs. Luminary ARM JTAG?
    ... the JTAG TRST pin connected, ... LM3S811 the TRST pin is left open. ... I also see that the Olimex board has a solderable bridge to connect TRST ... My liberal friends think I'm a conservative kook. ...
    (comp.arch.embedded)
  • Re: Use of TRST on ST vs. Luminary ARM JTAG?
    ... I notice that on the Olimex demo board for the STM32F103RBT6, ... LM3S811 the TRST pin is left open. ... Also if you want less signals in a JTAG header/cable. ... Some cables have separate MCU reset signal - perhaps this covers some that do not. ...
    (comp.arch.embedded)