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Thread: MCU <-> Mac & level shifting


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Permlink Replies: 2 - Pages: 1 - Last Post: Oct 29, 2012 7:33 PM Last Post By: Bunsen
bbraun


Posts: 493
Registered: 7/25/12
MCU <-> Mac & level shifting
Posted: Oct 22, 2012 10:41 PM
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I got my jlink working with a Keil MCB2300 dev board, using the Sourcery lite toolchain today, and was thinking about integrating that with my 030 PDS card.

One topic has been level shifting. The 030 PDS is 5V. The LPC2378 has 5V tolerant IOs, but that's only for input. For output, it's driving 3.3V, which will mostly work, but sometimes might not, and I really don't need to be debugging phantom issues like that. So, level shifting 3.3V output of the LPC2378 to the 5V of the 030 PDS.
I came across the 74HCT244, which seems to be pretty ideal. It's a tristate line driver, so it has the added advantage of tristating the data lines instead of consuming MCU cycles to change the GPIO lines to inputs when not addressed. The 74HC*T* is TTL compatible, so works with 3.3V inputs. It also has a /OE line to toggle the high impedance state of the entire chip, which could be driven by the address decoding logic. Or toggled by the MCU, if necessary.

Or even better, I've come across this for bidirectional communication: SN74LVC8T245
It looks pretty much designed for this task, although not available in DIP.

Message was edited by: bbraun
techknight

Posts: 110
Registered: 10/13/12
Re: MCU <-> Mac & level shifting
Posted: Oct 24, 2012 11:50 PM   in response to: bbraun in response to: bbraun
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im surprised anything is available in DIP anymore, moores law has pretty much killed that.
Bunsen

Posts: 39
Registered: 10/15/12
Re: MCU <-> Mac & level shifting
Posted: Oct 29, 2012 3:31 PM   in response to: bbraun in response to: bbraun
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Keil MCB2300 dev board

Interesting board. I've pretty much settled on the LPC[x] µcs for my own future projects - I mean, the bang for your buck is ridiculous. How much was the dev board?

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