Part Number: TCAL9539-Q1
Hi All,
I am using the tcal9539rtwrq1 part for my application. I am using the AVR microcontroller,
The IO expander controlled by AVR I2C Bus (400KHz operation).
Query: I want to know how much delay will cause to control the IO expander of IO lines by using I2C bus ? Mean typical delay to change or read the states of IO lines.
Regards,
Anbarasu S
Hi Anbarasu,
This is dependent on your I2C clocking speed.
Given 400kHz, and the following diagram for a write transaction
read transaction:
So about 3 bytes + start + stop for a write transaction (27 clock cycles)
about 4 bytes + start + repeated start + stop for a read (36 clock cycles)
THere are 9 clock cycles per i2c word - 8 bits + NACK/ACK
if operating at 400kHz
2.5 microseconds / clock period
write = 67.5 microseconds
read = 90 microseconds
This is only accounting for clock cycles, there is some delay between bytes and between write and read transactions, i2c buffering times, etc. total time might be more than these values, but these are estimates. Will these estimates work for your system?
Regards,
Tyler
