If you have zs(7D) serial ports on your machine, the synchronous devices may not exist. Look in the /dev directory for zsh (where h=0 and/or 1). If they do not exist, you can create them. Verify that the following two lines are in the /etc/devlink.tab file. If they are not there, add them.
type=ddi_pseudo;name=zsh zsh\M0 type=ddi_pseudo;name=clone;minor=zsh zsh
The white spaces in the lines above must be a single tab character before and after the zsh variables; using spaces will not work.
When these lines have been added to the /etc/devlink.tab file:
If this command does not work: