Reply With QuoteUse the +3.3v or +5v line on the decoders PSU, or you can use the 5v line from your PC's powersupply.
Are you trying to Jtag the ADB 9876 you posted about earlier? If so, you can't Jtag a 9876.
Dave
Jtagging
Morning all!
In the attached cct where do I find a 3.3v Vcc supply or do I use an external power supply?
TIA.........Leroy
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Use the +3.3v or +5v line on the decoders PSU, or you can use the 5v line from your PC's powersupply.
Are you trying to Jtag the ADB 9876 you posted about earlier? If so, you can't Jtag a 9876.
Dave
thanks mate. I was looking at jtagging to do a backup and 'practice' but have read that it appears not possible on this box. I see there is a 10 pin header on the main board though.Originally Posted by Dave001
Leroy
I had a couple of enquiries about what I used to jtag the 8776 with. I bought off Ebay.
It is very similar to the cct below
As pointed out in a post above, there is a 3.3v rail on the psu (there are many from 3.3V,5,12 up to 33V) where you can run power to the jtag board.
To make life easier I soldered right angled header pins on to the main board of the receiver.
I pulled the connector off an old IDE HD cable and cut it to accept 20 pins and soldered it to the cable that came with the jtag board keeping the leads as short as possible.
I had to remove the shell off the DB25 connector so it would mate with the parallel port on the laptop
You can find the apps and other files in other posts.
Leroy
Nice work Leroy.
Appreciate the feedback!
i have the same unit as well as one that i re-designed and have never had to use the 3.3-5v ever to connect and do what i had to do
The important thing with that circuit is to power it from the same voltage that the JTAG target is using. It depends on what the target device is: some processors want 3.3V, others 5V. Usually you'll find that voltage on the JTAG connector itself.
Also be aware that there's no standard pinout for all JTAG targets. Most devices using a given processor type (ARM, ST20, AVR, ....) use the same size connector and pinout as other devices using the same processor. But each processor is typically different. And there are occasionally exceptions. So it pays to always check the pinout - especially the supply voltage.
The adapter above is designed to be powered by the target. Some JTAG interfaces are powered by the host (the PC parallel port in this case), while a few have their own power supplies. You should always be clear about where the power is coming from.
Another issue that can bite you is the reset signal. Some systems need special links to be set or moved to allow reset to work. And other systems will only recognise the presence of the JTAG interface if you set or move a jumper link. JTAG is powerful but it's a higher level protocol and there is plenty of inconsistency from one system to another at the physical level, which is why you should always read documentation and learn all that you can before plugging things in!
And yes, you should keep the cables as short as possible!
i have built the above jtag circuit and can get jkeys to detect the proccessor but not the flash type i get the error reading dcu control register. The funny thing is that the above circuit only worked when i don't give it a supply voltage. the version is 2d so i assume i use the 8776a settings, the chip version's i read of the mb are toshiba 58FVB160AFT-70. I have never used jtag before has anyone used the above circuit before.
thanks shaun.
try erasing the flash before writing select 8776 , i also found it would connect
without adding in the power from the unit.
when i did it in the past i would erase the flash reboot the unit then write the new flash
The reason it works is the IC is drawing parasitic power from its inputs. The IC has protection diodes on each input designed to suppress overshooting transients; the diodes have the fortuitous side-effect of lifting VCC up to the highest input voltage. It's not good practice to rely on this side-effect because if you draw anything significant from any of the IC outputs you risk burning out the diodes. The ICs have VCC supply pins for good reason!
Best practice is to look for 3V3 (or 5V) on the receiver's JTAG connector and power it from that.
that's the problem i have tried 3v and 5v but it won't work the only way it detects the cpu is with no supply.like i said i get a read error and also i cannot load trap in programming has anyone built this cct before and had it working.
That's puzzling.
Some commercial JTAG products added feedback between certain port lines which their software looks for. In that way they try to make their hardware dongles unique, to prevent people from using their JTAG software without buying their particular brand of hardware. It's a long shot, but perhaps the software (or software configuration) you're using was expecting certain handshaking behaviour that the above JTAG circuit doesn't comply with, except fortuitously when powered only by port data lines.
Another possibility is that interface isn't handling reset signal correctly for that receiver. Many JTAG interfaces use an inverter stage for reset, such as . Without studying the receiver it's hard to know exactly what's going on, but perhaps the processor reset is being clamped, except when power is omitted.
Those are about the only explanations that come to mind. Someone else here may know for sure. Unfortunately I can't help with your reading errors because I don't have one of those receivers to play with. Good luck though. If nobody else has an answer then keep looking for other JTAG circuits which people have success using with that receiver - it may simply be that the design you're using is unsuitable. JTAGs ain't JTAGs and at a hardware level they aren't all interchangeable.
The can not load trap function could be due to a failed flash before hand.
i have seen this happen , what i suggest is
1: boot unit start jtag software select eeprom upgrade then make sue you select 8776 and flash the eeprom first
2: shut down software and power off completely the unit then re-power and start software
3: select the flash upgrade make sure you select 8776 and do the u4 first make sure you erase before upgrade.
4: now do the u8 flash .
wont i loose all my settings for colour etc if i flash it, the above schematic that i built is alittle bit different than the one i found that was posted before the crash.
i have changed the above circuit to this one with no success, anyone got a diagram of one they have built.
Some art work i put together
13666
Last edited by fandtm666; 13-03-09 at 01:20 PM.
Luck Duck (03-08-09)
thanks mate have you got an actual schematic for this i'm trying to trace everything to see whats different to mine i see there's 100n cap there?
little bit from here
and a little bit from here
Then some testing and building of various test boards
and final result the one i designed above that works as shown in pictures a few posts further up, though in the art work i have posted i have removed the 10 pin header which is shown in the picture further up on one of my prototype test boards
13666
i see you make your own pcb's any chance i could buy one off you as i have all the components. Send me a pm, it would be greatly appreciated
cheers guesty
dont forget to mirror the the images for printing if you downloaded the first version.
this version is ready for printing as is
this is it when all done
Last edited by fandtm666; 13-03-09 at 07:33 PM.
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