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9.7.5 Time Synchronization via Modbus
The rack time can also be sent using a Modbus command. The Modbus timestamp value is an epoch
timestamp and is the number of “tics” that have elapsed since January 1, 1970 at midnight. In the VC-
8000 one “tic” = 100 nanoseconds.
To learn more about epoch time, you can browse various converters and tutorials on the Internet (i.e.
http://www.epochconverter.com
).
Example: Set the VC-8000 time to Jan 1, 2020 9:00 AM PST.
SAM Setting Selection
Allow Status Register Writes
UTC -08:00 (Pacific Time)
Table 9-8) SAM settings (Modbus Time Synch)
• Calculate the epoch time for the time zone of the rack. In this example I am using the internet
to find a web page to convert to epoch time.
○ Jan 1, 2020 9:00 AM PST = 1,577,898,000 seconds
• Multiply by 10x7 to convert to tics (In VC-8000 one tic = 100 nanoseconds)
○ 15,778,980,000,000,000 tics
• Convert to Hex
○ 0038 0EE6 11D1 6800
• Use function code 16 to write registers. The word order in this example is Swapped. So, the
most-significant word (MSW) of the time value is in register 1009, and LSW is in 1012.
Table 9-9) Epoch time conversion example
• You can verify the time in the VC-8000 by viewing the event list. Press the reset button to
create an event and verify the time.
Figure 9-20) VC-8000 date, time shown in the Event List
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