It is the measurement of processor speed, 16millions instruction per second. As far as I know in Pic series clock is divided by 4 so 20 MHz means 5mips 40 MHz means 8mips. The problem is you need to respond serial clock which has a period of around 4 micro seconds. They do not use any known SPI or I2C serial interface.
Volkan
>-I use PIC 16F mcus at 20MHz and 18F mcus at 40 MHz, is that good enough?