Voltage levels with a XS1-G4 (XC-1A dev kit)

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simon
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Voltage levels with a XS1-G4 (XC-1A dev kit)

Postby simon » Tue Oct 05, 2010 9:09 pm

I'm a newcomer to the XMOS world, so apologies if my questions/requests for confirmation seem trivial. I want to interface my XC-1A kit to some TTL level signals, as well as an RS-232 port.

Vcc is 3.3V, however section 3.2 of the XS1-G4 says V(IH) can be between 2.0V&5.5V. This means I can apply a 5V TTL signal to the I/O pins without fear of damaging the device, and they will register correctly, yes? Similarly, TTL devices (such as 74XX family chips) will be happy with inputs at the 3.3V provided by the XS1-G4?

Secondly, to talk to RS232 devices I should use a chip such as a MAX232, correct?
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leon_heller
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Postby leon_heller » Tue Oct 05, 2010 9:33 pm

You should be OK interfacing TTL to the XS1-4G. Here is a useful document:

http://www.nxp.com/documents/application_note/AN240.pdf

You will need a MAX3232 for 3.3V operation.
simon
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Postby simon » Tue Oct 05, 2010 10:11 pm

So TTL->XMOS should be fine, but I'll possibly (depending on the chip family) need a level converter to bring me to 5V. In fact, I'll want to drive some 74HCTXX chips, so 3.3V looks to be OK for them. Do you have a recommendation for level conversion chips if I need to drive non-HCT CMOS logic?

Thanks for the info on the MAX3232.
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Berni
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Postby Berni » Wed Oct 06, 2010 5:18 am

You usually don't need logic around xmos chips and if you do just use stuff that runs on 3.3V, if you do need 5V for some reason you can get all sorts of level converter chips. You can also use certain gate familys for level conversion since standard TTL takes 2V as a high.

As for input yeah pins are 5V tolerant so you can apply 5V to it without a problem, however this feature is gone in all the L series chips so watch out.

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