) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. First Things First Chapter 1 Figure 1-1 Voltage representations of data as a 300-volt pulse, and the printer expects a 3-volt pulse, the two devices will have a brief (but exciting!) conversation, the ultimate result of which will be the release of a small puff of silicon smoke from the printer. Now they have to decide on a standard that they will use for actually originating and terminating the data that they will exchange. They are connected by a cable (Figure 1-2) that has nine pins on one end and nine jacks on the other. Logically, the internal wiring of the cable would look like Figure 1-3. However, when we stop to think about it, this one-to-one correspondence of pin-to-socket will not work. If the PC transmits on pin 2, which in our example is identified as the send data lead, it will arrive at the printer on pin 2-the send data lead. This would be analogous to holding two telephone handsets together so that two communicating par- ties can talk. It won't work without a great deal of hollering, since the handsets are oriented microphone-to-microphone and speaker-to- speaker! Instead, some agreement has to be forged to ensure that the traffic placed on the send data lead somehow arrives on the receive data lead, and vice versa. Similarly, the other leads must be able to convey information to the other end SO that normal transmission can be started and stopped. For example, if the printer is ready to receive the print file, it might put voltage on the data terminal ready (DTR) lead, which sig- nals to the PC that it is ready to receive traffic. The PC might respond by setting its own DTR lead high, as a form of acknowledgement, and then transmitting the file that is to be printed. The printer will keep its DTR lead high until it wants the PC to stop sending. For example, if the printer senses that it is running out of buffer space because the PC is transmitting faster than the slo