Jtag 510 without R21

[skutterbutt]

I'm trying to jtag a new 510 (used off ebay). My old 510 TRST location was just above R21. There is no R21 on this unit. Does anyone know where else to get TRST?

Thanks.

[skinerd]

Look closer, it just may have a jtag port.....I had one like that, felt like an idiot when I saw the port, after soldering to some tiny spots first.

[skutterbutt]

Duh. There is a jtag port. Thanks Skinerd. And yes, I also feel like an idiot.

[skinerd]

I have actually done that twice, just got used to seeing w/o port, that I just start soldering, then, damn........it's got a port.

[bartman0916]

hey skinerd, will a simple jtag work reliably with any of the 510's, I built a buffered one but cannot get it to work for some reason. I know this is a tiny bit off main topic sorry.

[skinerd]

hey skinerd, will a simple jtag work reliably with any of the 510's, I built a buffered one but cannot get it to work for some reason. I know this is a tiny bit off main topic sorry.

That is all I use now, simple jtag with 180 ohm resistors, never a problem here.

[bartman0916]

thanks Skinerd I'll go get some 180's tomorrow:)

[chep]

Why 180 ohms Skinerd? Is there something wrong or better vs the standard 100 ohms.

Also while on the subject..... what would be the issue if any of using say the 1/2 watt vs the 1/4 watt resistors as i have access to alot more of the 1/2 watt than the 1/4 watt ones.

[mrscig]

That is all I use now, simple jtag with 180 ohm resistors, never a problem here.

Hey Skinerd,
Do you think the 180 Ohm Resistors will be as noise free as a Buffered J-Tag? This will save lots of money if it's true.

[bartman0916]

I can field part of your ? chep, the 1/2 watt is overkill but will work fine its just physically bigger size. Im curious on the 180 ohm size as well, but I think its due to these only needing 3.3 volts vs the old boxes wanting 5 volts. More resistance would drop voltage a bit.

mrscig butter only protects your computer and receiver from killing each other should an mishap happen, other than that I dont know that its helps the noise any, but I could be wrong.

[chep]

Thanks for the reply bartman0916. I figured the 1/2 watt would be ok to use and have access to many of them is the only reason I asked. :)

Still wondering about the 180 vs 100 ohm though?

[skinerd]

Why 180 ohms Skinerd? Is there something wrong or better vs the standard 100 ohms.
Also while on the subject..... what would be the issue if any of using say the 1/2 watt vs the 1/4 watt resistors as i have access to alot more of the 1/2 watt than the 1/4 watt ones.

wattage is not important, we are talking current so low it really don't matter what wattage is used.
I use 180 ohm now, used to use 150 ohm until I went to buy and all they had was 180, so I bought and used, work fine. Actually anything 100 ohm up to 200 ohm should not be a problem....

[skinerd]

More resistance would drop voltage a bit.



Do you really understand voltage drops?? The current flowing in a jtag circuit is extremely small, voltage drop would be negligable. What the resistors do is serve as a current limiter, keeping the current small even in the event of different voltage levels in the receiver and the LPT port, to prevent one from damaging the other.

With E=IR, I=E/R, at 5v, with 180 ohm resistors, the max current flow would be about 28 miliamps, more than enough to jtag with.

[bartman0916]

Post #12 and 13 help
Thanks Skinerd, Learned something new again !
Never quite understood the resistor part in jtag setup, I do understand a bit more now.:)
5/ 100 = .05
5/ 150 = .034
5/ 180 = .0278
5/ 200 = .025