>________________________________
>
>I'm trying to embed a FT2232D based programmer into my board with a STM32
>(Cortex-M3 MCU).
>
>I want the programmer to be compatible with jtagkey, so I looked at schematics
>of compaible designs.
>
>I noticed that while the JTAG signals (TCK, TDI, TDO, TMS) are only buffered
>when translation is necessary, the SRST and TRST signals are always tri-state
>buffered, with OE going into the FTDI chip.
>
>Is there a reason for that? Can I omit the buffers?
>
>
Since
you are embedding the JTAG interface with the target, you can tell if
buffering is needed. We just went through a similar exercise and you
can pretty much hook everything up directly and use the FTDI MiniModule
layout (see commit from Rodrigo Rosa) if you target circuit is right.
Also, I heard it's possible to omit the TRST signal and only keep the SRST
signal, because system reset will also reset the TAP controller. Is that true?
Are there problems with that?
>
>TRST is optional since you can reset the JTAG TAP state machine with clocking
>TCK which TMS=1.
SRST might be needed for other reasons. For example some chips need it as part
of some kind of flash / code protection enable/disable.
Phil
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