evertz 8084 Instruction Manual page 138

Offset
Code
05
06
07
08
09
10
B.2.2 Daylight Saving Time
Daylight Saving Time (DST) was instituted to take advantage of the later hours of daylight between
April and October. In 1966, the U.S. Congress passed the Uniform Time Act that standardized the
length of Daylight Saving Time. For those parts of the United States that observe Daylight Saving
Time, it begins at 2 a.m. local time on the first Sunday of April. Time reverts to standard time at 2 a.m.
local time on the last Sunday of October. In the spring clocks spring forward by 1 hour to 3 a.m.; in the
fall clocks fall back by 1 hour to 1 a.m. Arizona, Hawaii and most of Indiana have chosen not to
observe Daylight Saving Time.
People often consider daylight saving time to be an "event" that happens twice a year, setting their
clocks ahead or back by one hour. In reality, DST is in effect (ON) for six months of the year and not in
effect (OFF) for the other six months, in regions that observe DST.
B.2.3 Calculating The Local Time
Local time can be calculated from UTC if we know the time zone we are in and whether daylight saving
time is in effect or not. (This is how VCRs are designed to arrive at local time.) Similarly we can
calculate UTC if we know the local time, the time zone and whether daylight saving time is in effect or
not. The following formula can be used to calculate Local time or UTC.
TZ is the Time zone offset according to the code in Table B-1.
DST has a value of 0 hours when Daylight Saving time is not in effect and the value of 1 hour when it is
in effect.
Local Time = UTC – TZ + DST
UTC = Local Time + TZ - DST
See section B.4.1 for information on how to set up the 8084AD correctly for either local time or UTC as
the LTC input. The 8084AD always transmits UTC in its time of day packets (see section B.3).
B.3 HOW XDS TIME OF DAY WORKS
XDS stands for extended Data Service. This data is encoded on Line 21 of field 2, using the same
format as closed caption information. It is intended to supply program related and other information to
the viewer. This may include the name of the program, content rating, name of the network, current
time of day, etc. EIA-608-B specifies that when there is caption or XDS information in field 2, then
there must be at least a null caption signal present in field 1 as well. The 8084AD automatically inserts
a null caption signal if there is no other caption signal present in field 1.
APPLICATION NOTE 3
Models 8084/8084AD/8085 Closed Caption Encoder Manual
Hours
UTC-05:00 Eastern
UTC-06:00 Central
UTC-07:00 Mountain
UTC-08:00 Pacific
UTC-09:00 Alaska
UTC-10:00 Hawaii-Aleutian
Table B-1: Time Zones in the United States
Revision 1.6.6
Time Zone Where Observed
New York
Chicago
Denver
Los Angeles
Alaska
Hawaii
AN3-2