ASCII/RS-485 Protocol Description
ASCII/RS-485 is based on a simple time protocol originally defined by Arbiter Systems called "ASCII + QUAL." An ASCII string is communicated over RS-485 (at 9600 bps) and consists of an on-time mark (OTM) transmitted once per second, followed by an ASCII representation of the date/time and time quality.
The ASCII code includes an ambiguity of one year, and so the device must first be set to the correct year through other means.
For more details on ASCII/RS-485 protocol and its applications, see Tech Note: Overview of ASCII/RS-485 Protocol (TN-108)
Time Sync: ION7550/7650 Power Meters
Modern industrial/commercial power systems require precise time synchronization of all devices to ensure meaningful data for analysis and reliable operation. ION7550 and ION7650 (and PowerLogic PM8000) power meters from Schneider Electric use ASCII/RS-485 protocol for precision time sync. CyTime™ SER-3200/2408 Sequence of Events Recorders from Cyber Sciences can generate ASCII/RS-485 to synchronize these meters, greatly simplifying time sync design. SER-3200/2408 Event Recorders accept a variety of time source options and then sync with each other using PTP. In turn, a PTP slave can also output a legacy protocol (e.g., ASCII/RS-485) to devices that do not support PTP.
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ION7550/7650 Time Sync Wiring
An ION7550/7650 (or PM8000) can accept ASCII/RS-485 time sync via a serial COM port. An SER-3200/2408 is configured to generate the ASCII signal via its built-in RS-485 interface, and can sync up to 16 meters.
Wiring of the RS-485 network follows the same conventions as any RS-485 2-wire network. The shield conductor should be grounded at one end only, and the data pair terminated with a suitable impedance, per the RS-485 standard.
ION7550/7650 (or PM8000) meters are configured for time sync via a serial COM port. Clock Source must be set to "COMM" and the COM port configured as follows:
- Protocol = GPS: Arbiter
- Baud rate = 9600 bps
- Serial Port Settings = 8N1
- RS-485 Bias = OFF
► For more details, see Tech Note: Overview of ASCII/RS-485 Protocol (TN-108)