EEVblog Electronics Community Forum
General => General Technical Chat => Topic started by: iamwhoiam on June 08, 2012, 09:49:09 pm
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Hi guys :)
Apart from Wikipedia, I can't seem to find any decent documentation (read: videos and how-to's) on exactly what comprises JTAG and protocols etc. I am looking at going into GSM repair and GSM repair solution design, and would need to be clued up on this.
Anything would help, so long as it's not too in depth to start with. Thanks :)
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JTAg : Joint Test Action Group is an orgaisatiion of industry professionals that seek to unify the test protocl , hardware and software used for in circuit debugging an device test.
They came up with IEEE 1532 and 1149.
1149 is for boundary scan while 1532 is for in circuit programming and testing.
Devices are connected in series and are essentially shit registers. you seriall shift in and out commands and data. The standard defines a number of fixed commands any device understands. you can read things like manufacturer , device code ( this lets you identify what oyu are talking to ) and a base command set that lets you toggle i/o pins so you can set and read pin states of the devices. this is used for board debug like testing electrical connections.
after that things become very complicated very quikcly. All other commands are device specific and you need the description from the device manufacturer for the instruction set and what it does ( sometimes signing NDA's is involved .. )
Real JTAG tesplatforms are very expensive.. Corelis Scanexpress is something you can use on Bench. the rest is dedicated machinery from Agilent , Teradyne , and others. these are big board tester machines.
The question is : what do you need it for ? if it is just to flash a rom you can get away with a simple tool like a Segger.
Rolling your own is an undoable task as you cannot get a hold of device documentation. most manufacturers do not release (unless nda's are signed ) the commandsets to the devices.
If it is really for board level testing ( the question is what testing ? contact testing you can do. that is standard in any device , but you will still need to analyse each and every device ... and build testsoftware per specific model / type phone .... ) beyond that ... ( like tracing code running through a jtag channel ) ... forget it.