  In this paper, we study the zero-error capacity of channels with memory,
which are represented by graphs. We provide a method to construct code for any
graph with one edge, thereby determining a lower bound on its zero-error
capacity. Moreover, this code can achieve zero-error capacity when the symbols
in a vertex with degree one are the same. We further apply our method to the
one-edge graphs representing the binary channels with two memories. There are
28 possible graphs, which can be organized into 11 categories based on their
symmetries. The code constructed by our method is proved to achieve the
zero-error capacity for all these graphs except for the two graphs in Case 11.
