> Is it safe to leave a TTL input floating. It is my understanding that
> they will pull high.

Will generally work OK floating BUT is bad practice and to be avoided. Will
sometimes catch you out and/or degrade performance if left floating. AFAIR
(a long time ago since I used 'real" TTL) ) they can be hard connected to
Vcc.

Be ware that this is for TRUE TTL - TTL compatible CMOS inputs may follow
quite different rules and should always be explicitly terminated.

                RM

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