CFGn() returns a 'configure n meters'
command byte corresponding
to the num_meters argument. num_meters
(valid values are 1 through 15)
specifies how many meters of cable are in your system. This is necessary in
before high speed non-interlocked handshaking (a.k.a. HS488) can be used on the bus.
The CFGn command byte must be preceded by a CFE command byte to take effect.