TWI and 11-bit I2C slave address devices

[tanekaf]

Hi. We are attempting to use the Infineon XMC1202 LED shield with our NRF52 device. The XMC1202 has an I2C address of 0x15E, instead of the traditional 7 bit address. We have been using the simple non-blocking TWI implementation to date. We can fake out the non-blocking TWI implementation for write commands. However for I2C reads, it is not clear how to pass in an address greater than 8 bits. Is this possible? Please advise.

[Jørgen Holmefjord]

Hi,

From the user manual of the shield I can see the following:

The RGB LED Shield’s I2C address is a 10-bit address and is pre-configured to be 0x15E. To address it, the master will send 2 bytes of address:

• The first 7 bits of the first byte are 11110XX, of which XX are the two most significant bytes of the 10-bit address. The 8th bit determines the read or write direction of the data transfer.
• The second byte is the lower 8-bits of the address.

This page describes the procedure for interfacing 10-bit addressable devices. If you setup a RXTX transfer where you write the second byte of the address before switching to TX mode, it should work. This is also described in section 3.1.11 in the I2C-bus specification and user manual.

Best regards,

Jørgen

[tanekaf]

Hi Jorgen. Thanks for the reply. I used the twi_scanner example to implement the TXRX suggestion. Code snippet below. nrf_drv_twi_xfer_desc_t xfer;

tx_buf[0] = lowerAddress;
tx_buf[1] = Command;  
       
xfer.type = NRF_DRV_TWI_XFER_TXRX;
xfer.address = upperAddress;
xfer.primary_length   = sizeof(tx_buf);
xfer.secondary_length = sizeof(rx);
xfer.p_primary_buf    = tx_buf;
xfer.p_secondary_buf  = rx;
err_code = nrf_drv_twi_xfer(twi_instance, &xfer, NRF_DRV_TWI_FLAG_NO_XFER_EVT_HANDLER);

This code works. I can read from the XMC1202. However, once this code is integrated into our platform that uses a soft device, the read fails. Specifically, the nrf_drv_twi_xfer() returns NRF_SUCCESS, but the rx_buffer is not populated. To test this theory, we added TWI to the ble_app_blinky example in ble_peripheral. Again, the read returns success, but the rx_buffer is not populated. Is there an issue with using this function with a softdevice?

[tanekaf]

Please disregard. Looks like we needed to enable TWI0_USE_EASY_DMA in our config file. That fixed the issue. Thanks again.