Plus if you setup the gating in such a way that the interrupts come after the capture edge in the microcontroller hardware timer/capture curcuit then there is virtually no difference in accuracy between the external circuit and the microcontroller approach. The microcontroller approach has the advantage in that the capture counts can be read directly from internal registers whereas for an external circuit you need some other interface to read back the counts, whether that be via some serial scheme, bus mapped on the XRAM connection or setup with bit banged nibble access.

The ONLY advantage I can ever see to an external circuit is that under some circumstances it could capture at higher resolution than a microcontroller design. The microcontroller timers clock at say 1 MHz for an old fashioned Intel 8051 whereas the external circuit can be designed for 10 or 20 MHz. The advantages of this are rapidly being lost because of the high speed processors such as the Cygnal parts where the timers have the ability to run at 50 MHz and more!!

Michael Karas