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Technical Resources

General introduction to serial protocols

National Semiconductors have a several very useful application notes which cover a lot of the basics of balanced serial communications. After, DMX512 is just a variant of RS-485, which is itself a superset of RS-422. These are PDF files, and the timestamp and size are as of September 1997. They don't look like they get updated that often, after all this stuff is all cast in stone...

AN-214: Transmission Line Drivers and Receivers for EIA Standards RS-422 and RS-423 (196 Kbytes; 02-Apr-96)

AN-216: Summary of Electrical Characteristics of Some Well Known Digital Interface Standards (151 Kbytes; 02-Apr-96)

AN-409: Transceivers and Repeaters Meeting the EIA RS-485 Interface Standard (130 Kbytes; 02-Apr-96)

AN-457: 'High Speed, Low Skew RS-422 Drivers and Receivers Solve Critical System Timing Problems' (114 Kbytes; 06-Jun-96)

AN-759: Comparing EIA-485 and EIA-422-A Line Drivers and Receivers in Multipoint Applications (87 Kbytes; 02-Apr-96)

AN-979: The Practical Limits of RS-485 (127 Kbytes; 02-Apr-96)

AN-1057: Ten ways to Bulletproof RS-485 Interfaces (151 Kbytes; 26-Oct-96)

The SN75156A

The SN75156A is a RS-485 transceiver chip, widely used for for both transmission and reception of DMX512.

The pinouts of the SN74156A can be obtained from Chipdir at Hitex. National Semiconductors also do a number of variants on the SN74156A, and their reference page for the DS16F95 has a useful PDF data sheet.

Doug Fleenor of Doug Fleenor Designs makes a case for using the SN74156B rather than the SN74156A in a newsletter (no longer online).