My company is building a device that is specified to have TTL outputs and I shall test them.
TTL 5V out: low <= 0.4V , high >=2.4V
LVTTL 3.3V out: low <= 0.4V , high >=2.4V
As you can see, there is no difference in the voltages between TTL and LVTTL.
So, as far as I understand, the difference is only internal, whether our ICs operate at 5V or 3.3V and thus the maximum voltage differs, which seems not important for outputs to work properly.
Given the device was implemented with LVTTL 3.3V technology, is it fully compatible to TTL technology and should I consider the test as passed or is there anything else I should consider, e.g. current?