tailieunhanh - Programming Serial and Parallel Ports

Programming Serial and Parallel Ports | 11 Programming Serial and Parallel Ports . Introduction Peripheral devices are usually external to the computer. Printers mice video cameras scanners data fax modems plotters robots telephones light switches weather gauges Palm Computing Platform devices and many others exist out there beyond the confines of your desktop or server machine. We need a way to reach out to them. The Java Communications API not only gives us that but cleverly unifies the programming model for dealing with a range of external devices. It supports both serial RS232 434 COM or tty and parallel printer LPT ports. We ll cover this in more detail later but briefly serial ports are used for modems and occasionally printers and parallel ports are used for printers and sometimes in the PC world for Zip drives and other peripherals. Before USB Universal Serial Bus came along it seemed that parallel ports would dominate for such peripherals as manufacturers were starting to make video cameras scanners and the like. Now however USB has become the main attachment mode for such devices. One can imagine that future releases of Java Communications might expand the structure to include USB support Sun has admitted that this is a possibility and maybe other bus-like devices. This chapter aims to teach you the principles of controlling these many kinds of devices in a machine-independent way using the Java Communications API which is in package . Conveniently ignoring things like internal modem cards on desktop machines This chapter was originally going to be a book. Ironic since my first book for O Reilly was originally going to be a chapter. So it goes. 306 . Introduction 307 I ll start this chapter by showing you how to get a list of available ports and how to control simple serial devices like modems. Such details as baud rate parity and word size are attended to before we can write commands to the modem read the results and establish communications. We ll move on to parallel printer