Hi! I am building a Z80 peripheral for an ECB bus device. All the Z80 control, data, and address bus signals are present on the ECB bus. However, the system clock (4MHz) signal is not available. The Z80 peripheral data sheets mention a "standard Z80 single-phase system clock" input to the CTC, DART, and PIO. I would like to supply a "local" 4MHz TTL oscillator can as an input to the CTC, DART, and PIO chips. Obviously, the "local" oscillator will not be exactly in phase or synchronized with the CPU clock. Do the Z80 peripherals require *the* CPU system clock or *a* system clock? I believe it is *a* system clock but do not know for sure and the documentation is not clear enough for me to tell. This is what the documentation says regarding the CTC Clock(phi) System Clock (input). This single-phase clock is used by the CTC to internally synchronize certain signals. If anyone knows *definitively* (not speculation) whether a "local" oscillator can serve as the CTC, DART, & PIO system clock and still work with the SBC CPU over the bus please let me know. Responses to this thread or send to my email. Thank you in advance Andrew Lynch