AN632 MAXIM [Maxim Integrated Products], AN632 Datasheet - Page 5

• Manufacturer Part Number: AN632
• Description: Evaluating the Accuracy of Maxim Real-Time Clocks (RTCs)
• Manufacturer: MAXIM [Maxim Integrated Products]

Other Accurate Time Alternatives
If your computer is not connected to the Internet, NIST also provides Dial-Up Time Setting
Service through a standard telephone line and analog modem. This service is called Automated
Computer Time Service (ACTS). With calibration, ACTS can set a computer clock with an
uncertainty of less than 10 milliseconds.
For more information about ACTS and to obtain software, see the following:
http://www.boulder.nist.gov/timefreq/service/acts.htm.
Alternately, you can get accurate time, all the time, by using a radio clock. Some are stand-
alone devices with a digital time display. These can often be interfaced to the PC with a serial
connection. For a list of radio clock manufacturers, see the following:
http://www.boulder.nist.gov/timefreq/general/receiverlist.htm.
A last alternative for calibrating your PC clock, and the least desirable in terms of ease of use,
is to use a regular voice phone line service to check the current accurate time. Such a service is
provided by the Time Service Department, U.S. Naval Observatory, Washington, D.C. The
Land Line Voice Time, without delay, is 900-410-TIME (50 cents the first minute, 45 cents a
minute thereafter). NIST time can be accessed over the voice phone line at [phone].
NISTIME 32: 32-Bit TCP Time Client
The main screen for the NIST TCP Time Client is shown in Figure 2. Selecting the Now option
in the Query Server drop-down menu will cause the current NIST time to be obtained and the
difference between the PC clock and NIST time computed, as shown in Figure 3. Clicking on
OK performs an adjustment of the PC clock to match NIST time. A verification of adjustment
then appears, as in Figure 4. Clicking on OK will remove this screen and return control to the
main screen for the NISTIME 32. If you are performing several cycles of calibration to reduce
the PC clock error in comparison to the NIST standard, you will need to wait between
calibrations until the message in the main screen changes from "No server selected" to a line
typically like "Server 2 selected using tcp port 13." At that time, another calibration can be
performed.
Figure 2. NISTIME 32 main screen
www.maxim-ic.com/an632
Page 5 of 8