5V and TTL interfacing

The ARMstamp can be directly connected to 5V TTL devices.  The output voltage for these ARM devices ranges from 0.4V to 2.9V when driving upto 4mA of current.  Most TTL devices will recognize these as valid logic levels (normally defined to be 0.8 and 2.0V) 

Inputs

The ARMstamp may also be directly connected to 5V TTL outputs.  If they are TTL compatable the voltage levels of the TTL output would normally be (0.4 and 3.4V), though they may go higher.  The inputs for these ARM devices are 5V compatable.

Tieing to Supply lines

The ARMstamp inputs may be connected directly to a GND pin, but if connecting to a fixed hight level, then it may be connected to a 5V supply line with a 1K or greater resistor.  This is the same recommendation for any TTL compatable device.  The reason being is that the 5V supply may exceed the 5V at times.