Chibi Consulting
Troubleshooting Serial CommunicationsOverview of Serial Communications
RS-422(EIA-422) and RS-485(EIA-485) are commonly used in the broadcast industry to communicate between equipment. The 422 protocol is used for point to point communications and the 485 protocol is used for multi-drop communications. These serial connections typically terminate on d-sub 9 pin style connectors.
These serial communications protocol utilize balanced pairs of connections for transmitted data and received data, as a result, 422 or 485 data paths can go a significant distance without problems. Even so, wiring issues can cause a significant amount of problems when setting up equipment. Most equipment that follows the SMPTE 207m standard will use d-sub 9 male to male cables wired straight through or pin to pin. If you want to make your own cables, keep in mind that the correct pairing is pins 2 & 7 with pin 6 as the shield for one pair and pins 8 & 3 with pin 4 as the shield for the other pair. Frame ground is on pin 1 & 9 with pin 5 designated as a spare.
The links below contain details for special cases which you may come across when setting up or troubleshooting communications with broadcast equipment.
Master Tributary reverser or 422 swap adapter
A 422 swap adapter is used to connect two devices wired as Master or two devices wired as Tributary together.
422 tap adapter
422 taps are used to monitor communications to troubleshoot problems.
Computer adapters
This adapters document link is so you can find various 422/485 adapters which are available if you need to interface to a broadcast device serially. Let me know if you find others that should be linked. contact 12 at chibiconsulting dot com
Reference
The SMPTE 207m standard covers communications over the RS-422 d-sub 9 interface and will be used as the wiring standard in this web site. You should read the SMPTE document in detail if you want to know more details about how the serial communications are intended to work.
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