I'm trying to interface LSM303CTR e-compass from ST-microelectronics with microcontroler. Due to design limitations I have to use 4-wire SPI.
This MEMS device has option to switch beetween 3-wire SPI/I2C by using ChipSelect pin (which I personally think is an absurd).
When CS is low - SPI is active, I2C is
endisabled and chip is selected
When CS is high - SPI is disabled, but I2C is enable
Here lies the problem. It I unselected chip by pulling CS high, I also enable I2C transceiver in MEMS device. But my MEMS sensor is connected to same bus with other devices. I have other devices on same bus (SD memory, LCD). I don't want to interfere with transmission from SD and LCD.
So here are my questions:
- How to safely interface 3-wire SPI with 4-wire SPI
- How mentioned I2C transceiver in MEMS device could interfere with my SPI bus while CS is high-state.