The outmost best solution for this issue is using a CPLD for the timing and triac firing.

- build a PLL circuit based on 4046 PLL device.
- use trigger from 50Hz/60Hz main power.
- build a 100 divider/counter in CPLD.
- build several compare registers in CPLD
- build parallel interface in CPLD to 8051 bus.


- use easy software in your controller. No timing or delay problems.


OR cheaper BUT difficult to maintain light stability.

- wire INT0 to your zerocrossing detector.
- write ISR INT0 routine to reset counter.
- init timer for 100 ticks in 10 ms.
- write ISR timer routine to increment counter.
- compare counter with internal registers for firing output connected TRIACS.

Have fun