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Hi Team,
Have a nice day!
Our device power supply is 1.8V and host output is 3.3V, therefore need to use level shifter, but I'd like to use 3-wire spi communication, unidirectional level shifter can't meet such requirement because 3-wire spi is bi-directional, so I need one bi-directional level shifter, seems SN74LVC2T45 supports this feature, could you please guide me how to implement bi-directional communication, just make pin5 DIR connect to host one GPIO to control high or low, is my understanding correct, thanks.
Best regards.
Hi Ladisch,
Thanks.
ok, my original thought is using two SN74LVC2T45, and control DIR low or high decide the direction, does this method work?
so TXU0304 can automatically switch direction right? no need to control by host.
No, the TXU has unidirectional channels. It does not work with this SPI variant.
But as far as I can see, you need only one bidirectional signal. So use the SN74AXC1T45, and something like the TXU0102 for the other two signals.
Yes, I understand, I checked SN74AXC1T45 datasheet, it clearly notes that for DIR, set to Logic High for A-to-B level translation, set to Logic Low for
B-to-A level translation.
So it's still need connect DIR to host one GPIO to control logic high or low, is this point correct. I just want to know if this method feasibility.
Thanks a lot!
Yes, it requires a separate direction control signal, which must be changed at the correct times.
The TXB0101 could do this without a direction control signal, but does not work with long traces/cables or pull-up/-down resistors.
Hi Ladisch,
Thanks a lot for your update, it's clear to me now, I will have a try.
Hi Ladisch,
Sorry for asking you last point, so normally I2C level shifter is bi-directional, like PCA9306 or TCA9617B, but there is no available level shifter or component specially for bi-directional SPI (3-wire SPI), like SN74AVC2T244 or SN74LVC2T45 actually have direction.
I²C uses open-drain signals, which are easer to level-shift.
The TXB can be used for SPI signals (with the limitations mentioned above).