Hello Herman,
There shouldn't be a problem using two separate crystals, one for each MCU. However, if you wish that the HCS12 provide a clock source for the HCS08 device, keep in mind the following -
- If you intend using FEE mode for the HCS08, the external frequency must not exceed 10MHz.
- If you use FBE mode (bypassing the FLL), the applied frequency has a maximum limit of 40MHz, but the maximum bus frequency would only be one half this frequency.
It would also be possible for the AW60 device to output a clock signal, via the MCLK pin, potentially to drive the HCS12 device. The maximum output frequency would be fbus/2. However, there might be an issue (for the HCS12) with the amount of jitter associated with the FLL signal.
Regards,
Mac