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Uart voltage level

 
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sturgessb



Joined: 25 Apr 2008
Posts: 246
Location: Norwich, UK
Posted: 20 July 2008, 2:38 AM    Post subject: Uart voltage level Reply with quote
quick question..

Looking at gps units and the one I'm interested in says it has a 2.8v uart for serial comms. Is this ok to Use directly with the zx24?

Ben
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dkinzer
Site Admin


Joined: 03 Sep 2005
Posts: 2499
Location: Portland, OR
Posted: 20 July 2008, 2:58 AM    Post subject: Re: Uart voltage level Reply with quote
sturgessb wrote:
t has a 2.8v uart for serial comms. Is this ok to Use directly with the zx24?
That voltage is probably not high enough to be reliably read as a logic 1 by the ZX. The threshold is 0.6 times Vcc so if you're running on 5.0 volts that's 3.0V minimum.

You should check the specification to see what the maximum voltage level is that the GPS device will tolerate. It could be that the output level of the ZX-24 is going to be too high for it.

In both cases, you could use the level converter circuitry that we've discussed previously.
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sturgessb



Joined: 25 Apr 2008
Posts: 246
Location: Norwich, UK
Posted: 20 July 2008, 12:28 PM    Post subject: Reply with quote
ok so the same principles apply then. I guess the sparkfun logic level converter I'm using for the spi would be ok. 5v down to 2.6v, and I think it would step 2.8 up to 4.x which is over the 3v logic high limit for the Zx.

Why so many voltage levels, will things ever standardize?
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dkinzer
Site Admin


Joined: 03 Sep 2005
Posts: 2499
Location: Portland, OR
Posted: 20 July 2008, 20:17 PM    Post subject: Reply with quote
sturgessb wrote:
Why so many voltage levels, will things ever standardize?
The various operating voltages are used to achieve different objectives. The 5-volt 74xx series TTL standard, in place since at least the early 70s, served a wide range of applications for a long time. But even during that time, there were other logic families like ECL and CMOS that had different supply voltages and different operating characteristics as well as different advantages and disadvantages.

More recently, in an attempt to achieve lower power consumption, devices were introduced that operate on lower supply levels, e.g. 3.3V, 2.8V and 1.6V.
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