  In digital systems such as fiber optical communications, the ratio between
probability of errors of type $1\to 0$ and $0 \to 1$ can be large. Practically,
one can assume that only one type of error can occur. These errors arecalled
asymmetric. Unidirectional errors differ from asymmetric type of errors; here
both $1 \to 0$ and $0 \to 1$ type of errors are possible, but in any
submittedcodeword all the errors are of the same type. This can be generalized
for the $q$-ary case. We consider $q$-ary unidirectional channels with feedback
and give bounds for the capacity error function. It turns out that the bounds
depend on the parity of the alphabet $q$. Furthermore, we show that for
feedback, the capacity error function for the binary asymmetric channel is
different from the symmetric channel. This is in contrast to the behavior of
the function without feedback.
