the problem is, the spi device is far away from the mcu. it's quite unstable.

3.3V MCU SPI clk/data --------- >1.5m track---------> device

someone suggested me to use a buffer(74hct245) to convert 3.3v signal to 5V and add pull-up resistors.

3.3V MCU SPI clk/data -->74hct245-->5V pull-up res --> device


i really need more advice.
thx.

 

How fast is the clock that you are using. The use of a driver chip with more current drive will help on a long cable which looks like a capacitive load. Using a Schmitt Trigger on the input will help also.

A better solution might be to use a differential line driver and receiver. Proper termination of the transmission line will also help to control reflections.

 

How fast is the clock that you are using. The use of a driver chip with more current drive will halp on a long cable which looks like a capacitive load. Using a Schmitt Trigger on the input will help also.

A better solution might be to use a differential line driver and receiver. Proper termination of the transmission line will also help to control reflections.

thx for your reply.
I use a schmitt trigger buffer NL27WZ17. And it works!
http://www.onsemi.com/pub_link/Collateral/NL27WZ17-D.PDF