Clock Transition Times
The manufacturers specify the maximum transition times (rise time and fall time) for the output to respond properly. If these specified figures are exceeded, the flip-flop may respond erratically or even may not respond at all. This parameter is logic family specific and is not specified for individual devices. The allowed maximum transition time for TTL devices is much smaller than that for CMOS devices. Also, within the broad TTL family, it varies from one subfamily to another.
Maximum Clock Frequency
This is the highest frequency that can be applied to the clock input. If this figure is exceeded, there is no guarantee that the device will work reliably and properly. This figure may vary slightly from device to device of even the same type number. The manufacturer usually specifies a safe value. If this specified value is not exceeded, the manufacturer guarantees that the device will trigger reliably. It is 34 MHz for 74ALS109A.
