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Is Cygnal JTAG/C2 Interface EMI Vulnerable

Started by Klaus Vestergaard Kragelund March 13, 2004
Hi
I'm using a 80C51F302 Cygnal device and I have based the design on what I've
read on the Cygnal site that C2 is the way to go for such a pin-limited
device.

Well in the forum on the site some have commented that the JTAG interface is
vulnerable to noise and 4k7 pull-up/down are recommended. But using a
low-power device and putting load resistors on the signals seems futile to
me.

If I only use the C2 interface, can I disable the JTAG interface to discard
the pull-downs?

And what are your experiences on this NG?

Thanks

Klaus Kragelund


"Klaus Vestergaard Kragelund" <klauskvik@hotmail.com> wrote in message
news:40530a1b$0$228$edfadb0f@dread12.news.tele.dk...
> Hi > I'm using a 80C51F302 Cygnal device and I have based the design on what
I've
> read on the Cygnal site that C2 is the way to go for such a pin-limited > device. > > Well in the forum on the site some have commented that the JTAG interface
is
> vulnerable to noise and 4k7 pull-up/down are recommended. But using a > low-power device and putting load resistors on the signals seems futile to > me. > > If I only use the C2 interface, can I disable the JTAG interface to
discard
> the pull-downs? > > And what are your experiences on this NG? > > Thanks > > Klaus Kragelund > >
If you put pull-up resistor on C2CK line, that should do the trick. As C2CK (RESET) pin is an input, there's no current flowing, so there won't be any increase in current consumption.... So, it won't affect device's low-power specs. Also, C2 interface is NOT JTAG interface. It's Cygnal's proprietary two-wire debug interface. F3xx devices have ONLY C2 interface. Bigger devices have JTAG interface. If you have any other questions, you have my e-mail address (remember HP34401 serivce manual ?) :)) - Dejan
"Dejan Durdenic" <no_spam@nospam.com> wrote in message
news:c2v5vf$3ua$1@ls219.htnet.hr...
> > "Klaus Vestergaard Kragelund" <klauskvik@hotmail.com> wrote in message > news:40530a1b$0$228$edfadb0f@dread12.news.tele.dk... > > Hi > > I'm using a 80C51F302 Cygnal device and I have based the design on what > I've > > read on the Cygnal site that C2 is the way to go for such a pin-limited > > device. > > > > Well in the forum on the site some have commented that the JTAG
interface
> is > > vulnerable to noise and 4k7 pull-up/down are recommended. But using a > > low-power device and putting load resistors on the signals seems futile
to
> > me. > > > > If I only use the C2 interface, can I disable the JTAG interface to > discard > > the pull-downs? > > > > And what are your experiences on this NG? > > > > Thanks > > > > Klaus Kragelund > > > > > > If you put pull-up resistor on C2CK line, that should do the trick. As
C2CK
> (RESET) pin is > an input, there's no current flowing, so there won't be any increase in > current consumption.... > So, it won't affect device's low-power specs. Also, C2 interface is NOT
JTAG
> interface. It's > Cygnal's proprietary two-wire debug interface. F3xx devices have ONLY C2 > interface. Bigger > devices have JTAG interface. If you have any other questions, you have my > e-mail address (remember > HP34401 serivce manual ?) :)) >
Great Dejan, thankyou for your answer :-) Wrt the HP34401A - Isn't great with usenet - I help you, and suddenly you help me too in need *S* Well, back to the Cygnal device: Do you know the situation of the larger devices (F02x). They run with JTAG and if they need pull-ups they will use power for that since the JTAG doesn't reside on the Reset pin Moreover why not run with the C2 interface on the larger devices too? If its equally capeable as the JTAG? Thanks Klaus
> Great Dejan, thankyou for your answer :-) > > Wrt the HP34401A - Isn't great with usenet - I help you, and suddenly you > help me too in need *S* > > Well, back to the Cygnal device: > > Do you know the situation of the larger devices (F02x). They run with JTAG > and if they need pull-ups they will use power for that since the JTAG > doesn't reside on the Reset pin > Moreover why not run with the C2 interface on the larger devices too? If
its
> equally capeable as the JTAG? > > Thanks > > Klaus > >
Bigger devices do have JTAG interface (4-wire). They use dedicated pins and again you can pull-up CLK pin and that should do the trick as JTAG state machine changes states only on the rising edge of CLK. There will be no power consumption penalty as the CLK pin is an input - so no current will flow...Unfortunately you cannot choose which interface to use - bigger chips have JTAG, smaller ones C2... - Dejan

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