I2CSPI

I2CSPI refers to a class of bridge devices and firmware that translate between I2C and SPI protocols. The goal is to enable devices that use I2C to communicate with devices that use SPI, or to connect SPI devices to an I2C host, without redesigning existing hardware. I2CSPI solutions can be implemented as dedicated bridge ICs, as firmware in microcontrollers with appropriate peripherals, or as standalone bridge modules.

Most I2CSPI bridges expose two interfaces: an I2C interface on one side and an SPI interface on the other. The bridge contains a control processor, buffering logic, and bus translators, and may include level shifting and, in some cases, galvanic isolation. On the I2C side, the bridge acts as a master or slave depending on design, often handling I2C addressing and multi-master considerations. On the SPI side, it presents the conventional MOSI/MISO/SCK/CS signals and supports common SPI mode variants (CPOL/CPHA) and clock rates. Some designs support configurable mappings so multiple SPI devices can be accessed via a single bridge.

Performance is typically limited by the slower of the two buses and by bridge overhead, resulting in lower throughput and higher latency compared with native SPI or I2C connections. Not all I2C features, such as repeated starts or multi-master arbitration, map cleanly to SPI, so compatibility should be evaluated.

Common use cases include sensor hubs, microcontroller ecosystems that mix I2C and SPI peripherals, and applications requiring isolation or level shifting between buses. Vendors in the semiconductor industry offer I2CSPI bridges as both standalone chips and integrated functionalities within microcontrollers.