AN-214 Datasheet | National Semiconductor

Transmission Line Drivers and Receivers for TIA/EIA Standards RS-422 and RS-423 Transmission Line Drivers and Receivers for TIA/EIA Standards RS-422 and RS-423 Introduction With the advent of the microprocessor, logic designs have bee both sophisticated and modular in concept. Frequently the modules making up the system are very closely coupled on a single printed circuit board or cardfile. In a majority of these cases a standard bus transceiver will be adequate. However because of the distributed intelligence ability of the microprocessor, it is being mon practice for the peripheral circuits to be physically separated from the host processor with data munications being handled over cables (e.g. plant environmental control or security system). And often these cables are measured in hundreds or thousands of feet as opposed to inches on a backplane. At this point the ponent wavelengths of the digital signals may bee shorter than the electrical length of the cable and consequently must be treated as transmission lines. Further, these signals are exposed to electrical noise sources which may require greater noise immunity than the single chassis system. It is the object of this application note to underscore the more important design requirements for balanced and unbalanced transmission lines, and to show that National’s DS1691 driver and DS78LS120 receiver meet or exceed all of those requirements. National Semiconductor Application Note 214 John Abbott John Goldie August 1993 tor’s application note AN-108 and TIA/EIA standards TIA/ EIA-422-B (balanced) and TIA/EIA-423-B (unbalanced). In this application note the generic terms of RS-422 and RS-423 will be used to represent the respective TIA/EIA standards. A summary review of these notes will show that the controlling factors in a voltage digital interface are: 1. 2. 3. 4. The cable length The data signaling rate The characteristic of the interconnection cable The rise time of the signal The Requirements The...