"H" schrieb im Newsbeitrag news: snipped-for-privacy@news-server.san.rr.com...
Hi.
>
> I'm working on a microcontroller app. An SPI peripheral only works at
> 3.3V while the micro only wants 5V. This SPI has to be bi-directional.
>
> I'm trying to figure out a cost effective way of interfacing the two.
> Micro's SPI pins are not open-drain. Trying to make it power efficient,
> this is battery powered.
>
> Most simple level translators are NPNs, but that ends up with voltage
> inversion...maybe mess with CPHA and CPOL?
>
> Voltage divider on 5V micro output and use a blocking diode + pull-up to
> go from 3.3V to 5V? SPI needs to run at 1 MBit+.
>
> Ideas?
>
> H.
Straight forward (and maybe boring) solution:
Use 3/4 74AHC125 or VHC125 (VCC connected to 3,3V) to translate levels for spice,spiclk,spimosi. These chips allow higher input levels as their VCC:
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Use a single gate HCT125 (VCC connected to 5V) buffer for spimiso.
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MIKE