Generally, 3.3V TTL signals will have a suitable voltage cross-over with 3.3V CMOS and therefore, the TTL signal can be used to trigger the CMOS device.
The logic level thresholds for 3.3V CMOS are a known standard. For a 3.3V CMOS device to acknowledge a logic high or low, the required voltages are as follows:
- Logic low - input must be between 0V and 0.8V.
- Logic high - input must be between 2V and 3.3V.
To be certain of whether your TTL output is compatible with your CMOS device, refer to your device's specifications sheet.