Comparing JTAG, SPI, and I2C

This Spansion application note discusses three popular serial buses: JTAG, SPI, and I2C. A typical electronic product today will have one or more serial buses in them.

Using a serial bus in a system has many advantages over a parallel bus: lower component cost, smaller PCB; simplified design and typically, lower power consumption.

The trade-off for these advantages is inherently lower data transfer rates than a parallel bus system. In serial buses only one wire carries data into and/or out of the device. In some cases there is one signal for carrying data into the device another different signal for carrying data out of the device. On the other hand in parallel buses many signals transfer data simultaneously into and out of the device.

View the PDF document for more information.