Combining SDI and SDO and interfacing two devices with diffrent voltage levels.

[RoboWanabe]

HI

Ive searched the forum and cant find anyone who has had a similar problem so going to throw this out there.

Ive been given a task to implement this circuit:



the main problems are:

1) Im using a pic18f45k20 which dosent have a 5v output and i belive im going to have an issue with interfacing the two devices i.e. digital interfacing with two diffrent voltage levels?

2) i have two pins SDI and SDO and in the circuit they are combined into one. Am i right in thinking that i need to create the mosfet circuit on MCU side my self? also if i send data isnt MISO going to recive at the same time? do i release or ignoe the PIN when transmutting.

3) what do i need to find out about each device to interconnect them i.e input thresholds etc

Thanks guys.

 

[ericgibbs]

hi,
Have a look thru this pdf.

E

 

[RoboWanabe]

Hey thank you so much ill have a look at that but might struggle understanding it lol

 

[Diver300]

I don't think that there will be any problem using the circuit that you suggest. The pull-up is to 3.3 V, and the SPI signals are all open-drain, so they either pull down or do nothing. The 3.3 V that they will get to will be fine for the 5 V supplied device. It probably has a threshold at 1.5 V or so anyhow.

 

[RCinFLA]

Take a look at ST Micro ST2378E. Bidirectional level translator.