Question

consider that you need to set up a serial network, which will have one Master and four Slaves. Either SPI or I2C can be used. Every second, data has to be distributed, such that one byte is sent to Slave 1, four to Slave 2, three to Slave 3, and four to Slave 4. If the complete data transfer must take not more than 200 us, estimate the minimum clock frequency which is allowable for SPI and I2C. Assume there are no other timing overheads

Answer 1

Answer:- Assuming no other timing overhead than data transfer, we can say that in 200 micro second we need to transfer all the the data bytes to the slave.

Number of bytes transferred = 1 + 4 + 3 + 4 byte = 12 bytes

So number of bits transferred = 12x8 bits = 96 bits. Total time = 200 us = 0.0002 s. Thus bits per second i.e frequency of signal(minimum) must be, f = 96/0.0002 Hz = 480000 Hz = 480 kHz.

NOTE:- If we follow proper I2C or SPI protocol for data transfer we need to send some other data bytes such as slave address in I2C, address of loaction to read/write etc., in that case calculation may change but as we are not considering those parts here, the above value of frequency is the minimum requirement.