JTAG level shifters

What is commonly used for JTAG level shifting?

I have an application where I need to convert a small number of
signals from low-voltage TTL levels to "normal" TTL levels.

It's very similar to a JTAG port where you have signals going in both
directions and a reference signal indicating what the logic levels
are.

Modern CPLD's have Vccio pins, but that would be overkill for the
number of signals I have.

Any suggestions?

TIA,
G.

On 13 Apr 2007 11:54:17 -0700, ghelbig@lycos.com wrote:

>What is commonly used for JTAG level shifting?
>
>I have an application where I need to convert a small number of
>signals from low-voltage TTL levels to "normal" TTL levels.
>
>It's very similar to a JTAG port where you have signals going in both
>directions and a reference signal indicating what the logic levels
>are.
>
>Modern CPLD's have Vccio pins, but that would be overkill for the
>number of signals I have.
>
>Any suggestions?

Depending on your exact voltage levels, you can use 74HCT device
powered from 5V to do the conversion for the output signals, and a
74HC device powered from your low voltage to do the conversion from
the normal TTL signals to the low voltage. This works for voltages
down to 2V.

Regards
  Anton Erasmus

Anton Erasmus <nobody@spam.prevent.net> wrote:
> On 13 Apr 2007 11:54:17 -0700, ghelbig@lycos.com wrote:

> >What is commonly used for JTAG level shifting?
> >
> >I have an application where I need to convert a small number of
> >signals from low-voltage TTL levels to "normal" TTL levels.
> >
> >It's very similar to a JTAG port where you have signals going in both
> >directions and a reference signal indicating what the logic levels
> >are.
> >
> >Modern CPLD's have Vccio pins, but that would be overkill for the
> >number of signals I have.
> >
> >Any suggestions?

> Depending on your exact voltage levels, you can use 74HCT device
> powered from 5V to do the conversion for the output signals, and a
> 74HC device powered from your low voltage to do the conversion from
> the normal TTL signals to the low voltage. This works for voltages
> down to 2V.

You can also look for the 74LVC1/2/8T45. 
-- 
Uwe Bonnes                bon@elektron.ikp.physik.tu-darmstadt.de

Institut fuer Kernphysik  Schlossgartenstrasse 9  64289 Darmstadt
--------- Tel. 06151 162516 -------- Fax. 06151 164321 ----------

On Apr 13, 1:39 pm, Uwe Bonnes <b...@hertz.ikp.physik.tu-darmstadt.de>
wrote:
> Anton Erasmus <nob...@spam.prevent.net> wrote:
> > On 13 Apr 2007 11:54:17 -0700, ghel...@lycos.com wrote:
> > >What is commonly used for JTAG level shifting?
>
> > >I have an application where I need to convert a small number of
> > >signals from low-voltage TTL levels to "normal" TTL levels.
>
> > >It's very similar to a JTAG port where you have signals going in both
> > >directions and a reference signal indicating what the logic levels
> > >are.
>
> > >Modern CPLD's have Vccio pins, but that would be overkill for the
> > >number of signals I have.
>
> > >Any suggestions?
> > Depending on your exact voltage levels, you can use 74HCT device
> > powered from 5V to do the conversion for the output signals, and a
> > 74HC device powered from your low voltage to do the conversion from
> > the normal TTL signals to the low voltage. This works for voltages
> > down to 2V.
>
> You can also look for the 74LVC1/2/8T45.
> --
> Uwe Bonnes                b...@elektron.ikp.physik.tu-darmstadt.de
>
> Institut fuer Kernphysik  Schlossgartenstrasse 9  64289 Darmstadt
> --------- Tel. 06151 162516 -------- Fax. 06151 164321 ----------- Hide quoted text -
>
> - Show quoted text -

That looks like a good fit; thanks.