ISM330DLC - 3 wire SPI mode

[KJose.1]

Hi,

How does the 3 wire SPI mode work in ISM330DLC? How is the physical connection for this mode? Are there any changes to be made in register configuration other than enabling SIM bit in register 12h?

Regards,
KJ

[Federica Bossi]

Hi ​@KJose.1 ,

You can refer to AN5125

In 3-wire SPI mode, the device uses:

• CS on pin 12
• SPC/SCK on pin 13
• one single bidirectional data line on pin 14 (SDA)

Pin 14 is SPI serial data input (SDI) and, in 3-wire mode, also serial data output (SDO), which means the same pin is used for both transmit and receive.

The SIM bit in CTRL3_C (12h) selects the SPI mode:

• SIM = 0 → 4-wire SPI
• SIM = 1 → 3-wire SPI

Therefore, the physical connection for primary 3-wire SPI is:

• MCU CS → ISM330DLC CS
• MCU SCK → ISM330DLC SPC
• MCU bidirectional SPI data line (SDIO) → ISM330DLC SDA

Pin 1 (SDO/SA0) is the dedicated output pin for 4-wire SPI, while in 3-wire SPI the shared data line is pin 14 (SDA). When SIM = 1, a pull-up is enabled on pin 1.

As for the register configuration, the only setting required to enable primary 3-wire SPI is the SIM bit in CTRL3_C (12h).