Valid only with cbLoopbackCode = latchDS0Drop.
DSP-OP devices can be cross connected in the central
office in a daisy chain. By this, the user has
capability to put any of the devices in the chain in
loopback mode. A value of 1 results in no iteration
and will cause the very first device in chain to go
into loop back. A value of 2 will result into one
iteration and will cause the second device to
go into loopback and so on. This tests the channels
across multiple devices connected in a chain.