SPI Level Translation

[Black_Hawk]

Hi all !

I'm trying to connect an S12X running as master with an LPC2138 as slave over SPI. The S12X is powered at 5v and the LPC at 3v3. Do i have to do some sort of level translation between the two?

If yes, could someone post any advice ?

Thank you,

James

[bigmac]

Hello,

My understanding is that the LPC2138 has "5 volt tolerant" inputs.  Therefore, level translation should not be necessary for any output from the S12X, including the MOSI, SCK and /SS signals originating from the master.  This leaves the MISO signal, originating from the slave, with a 3 volt logic swing, that may need level translation to increase the logic high level.  A buffer with TTL compatible input should be suitable.

Regards,

Mac

[rocco]

. . . or for MISO, a pullup resistor to +5v may be all that is needed. I don't have the specifications for the LPC2138, so I don't know if it allows 5 volts on it's output.

[Black_Hawk]

Hello!

Thanks for your replies.

I've ordered some level translators from Analog Devices ADG3308 and from TI TXB0104. I'll receive them next week and see how it works. I've tried with a +5v pullup but it doesn't work.

Anyway... i hope it will work with the translators. I'll let you know in a few days.

Thanks again and a HAPPY NEW YEAR !!!

James

[Alban]

Hello,

There is an Application Note explaining level translation on S08, but it also applies.

AN2433.

You can also run the S12X at 3.3 Volt to avoid level translation with the SPI.

Alban.