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MSP430 Ultra-Low Power 16-bit Microcontroller Forum
Sharing JTAG pins to flash multiple MCUs
Despite the fact that I've been programming MSP430 for some years, this is my first post on this forum :)
My question is:
Imagine you have a pcb with more than one MSP430. Can I wire the JTAG pins (TDI, TDO, TMS, TCK, RST) of all MCUs in parallel and use a jumper on the TEST pin of each MCU to choose which one I want to work with (flash/debug) ?
NOTE: I assume that the JTAG pins are only used for that (no I/O use by the program)
Mário Martins de Sousa
If the TEST pin is left floating, the JTAG pins revert to normal port pins. This may or may not have influence on the JTAG performance (leakage currents, impedances etc.).So my answer is an authoritative "maybe" :)
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Thank you Jens-Michael for your quick answer!
Anyway I don't believe that no one ever tried to do something like that :) Just wanted to know if it works or not to avoid wasting time building a pcb.
I think it is useless test it with some PDIP package MSP430s on a breadboard since I don't know if the 5xxx or 6xxx families will behave the same way.
The typical application for multiple MSPs attached to one programmer is production programming wiht a GANG programmer. But here, usually each attached processor is on its own PCB and therefore separately connected.
On the experimenters board with a 4x and 2x processor, there are two independent JTAG headers, not just a jumper. So it seems that indeed nobody has tried that yet.Earn a badge as multi-processor-JTAG pioneer. :)
Hello!For future reference this kind JTAG sharing works!You just have to place a jumper on each TEST pin to choose what uC you want to flash. I've used two F5436A and one F5638 and it worked with no problem. I've placed also a jumper on RST pin to be able to reset only one uC at a time (usefull for debug).;-)
Did someone of you try to do that JTAG sharing with uCs with dedicated JTAG pins (no TEST pin)?
In this document:http://www.ti.com/lit/ug/slau320d/slau320d.pdf
Page 22, section 126.96.36.199 "Fuse Check and Reset of the JTAG State Machine (TAP Controller)" it says:
“Each MSP430 family device includes a physical fuse used to permanently disable memory access viaJTAG communication. When this fuse is programmed (or blown), access to memory via JTAG ispermanently disabled and cannot be restored. When initializing JTAG access after power up, a fuse checkmust be done before JTAG access is granted. Toggling of the TMS signal twice performs the check.While the fuse is tested, a current of up to 2 mA flows into the TDI input (or into the TEST pin on deviceswithout dedicated JTAG pins). To enable settling of the current, the low phase of the two TMS pulsesshould last a minimum of 5 μs.”
So it means that on the devices that have dedicated JTAG pins (no TEST pin), the TDI line is acting more or less like TEST line on devices with shared JTAG pins?If we disconnect TDI line from MCU, then the fuse checking will fail and the access to flash memory won’t be granted – JTAG for this specific MCU will be turned off.
But what about the other lines, for instance TDO. If I disconnect TDI and fuse checking will fail for one of the uC, will there be some feedback signal on TDO from MCU after fuse checking failure? Then it could override the TDO line between programmer and uC that I want to have acces to.
I will appreciate any helpful tips.
Thank you for the answer.
So, there is no way to share the JTAG in some simple and easy way (by switching just 1 line instead of 4)?
How about putting one of the MCUs into the reset state while the other one is being programmed? Will it work?
Mariusz WysoczanskiSo, there is no way to share the JTAG in some simple and easy way (by switching just 1 line instead of 4)?
So in theory, you can daisy-chain all JTAG peers. The software, however, needs to precede the JTAG commands by the appropriate number of pass-through commands then. And this is not supported by MSP430LIB and the FETs.
Mariusz WysoczanskiHow about putting one of the MCUs into the reset state while the other one is being programmed? Will it work?
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