Hi Vikrant,

a) What maximum frequency that I can give with the combination of CPLD+89c52 for two channels

The timer/counters of the 89C52 will be of no use in this case; you will have to use the external interrupts to detect the falling edges of the CLK. Then in the interrupt routine increment or decrement a software counter based on the direction signal. The time the ISR takes will determine the max. count frequency. This time depends on the clockfrequency you run your 89C52 at.

b) If I am using the 89c52 timers for other work and I use external counters from CPLD how much it will affect the max. Frequency.

In this case the limitation is the speed of the CPLD, which is very, very fast. Counter frequencies of tens of MHz are no problem.

c) can u suggest any better solution ?which should not be costly.

Personally I would choose the solution with CPLD counters. Can't think of a better one :o)

Regards,
Rob.