On a healthy and bare Amstrad CPC, &FF is the value you can usually read on the DATA bus in high impedance state. On a healthy and bare Amstrad Plus, this is usually &78. This property has been used to detect the Plus machines in several productions (and failed on several occasions as this is not a reliable technique) [https://www.grimware.org/doku.php/documentations/devices/io.devices#blind.test Source].
<b>You should never do anything relying on the value of the DATA bus in High impedance state and expect it to work the same on all machines. It won't!</b>
[[Category:Emulator]] [[Category:Programming]]