Configuring a Port
If any default condition is to be changed, the port must be configured before it is used. Configuring a port is accomplished by one or more commands described in this section. There are three principal commands Each of these three is concerned with several configuration variables The parameters of the commands are coded to signify different values of the several variables The details of the coding are presented in the Appendices A particular default condition is Block Output Mode in which of course you can not input data. To input from a port you must put it into concurrent I/O mode with the START CONCURRENT I/O command. Thus the START CONCURRENT I/0 command is a configuration command. It is different from the other configuration commands in that the port to which it applies must be OPENed first. Moreover, it is much more complex than other configuration commands. You should think of the START CONCURRENT I/0 mode command as being a configuration command in one aspect, and as having more important effects on other aspects of using the configured port, and, indeed, all the ports.