PC Serial Peripheral Design (3)

In this third part we look at the output signals of the RS-232 interface. In order to control devices with these output signals, it is necessary to know what can (and what cannot!) be expected of the output drivers: this knowledge can then be used in our experiments.We have already seen in this course that the output signals of the RS-232 interface swing between –10 V and +10 V. However, because the output current is limited, it is safe to connect an LED directly. But what exactly are the characteristics of the outputs? We shall attempt to answer this question now.In general, manufacturers of PC equipment follow the RS-232 standard, in which the voltage levels used to send data are specified. It was originally specified that the output voltages should be ±15 V, while at the inputs a signal of at least ±3 V is required.