M e r i d i a n I I U s e r M a n u a l
189
"Smarter Timing Solutions"
Appendix
H
Time Code Formats
A standard feature of your Meridian II Precision TimeBase is a single time code output available
at the rear panel BNC connector identified as AM CODE. A DC-shift time code is available as an
optional output on the CPU Module (see
CPU Module Options
in
Chapter 10 - Optional Rear-Panel
Outputs
). Multiple time code outputs (both AM and DC-shift) are also available via an option board
module (see
Plug-In Module Options
in
Chapter 10
).
The output code format is selectable via the front-panel user interface. See
Time Code Output Setup
in
Chapter 12 - Front-Panel Keypad and Display
. You can also select the time code format via a
console command. See
CpuOptsConfig
in
Chapter 3 - Control and Status Commands
. Each format
is described below. Time codes are commonly used to provide time information to external devices
such as displays, magnetic tape devices, strip chart recorders and several types of embedded com-
puter peripheral cards.
IRIG-B122/002
This is the most widely used format and is normally the factory default for the AM Code output. The
IRIG-B122 format is a 100 bps code and is used to amplitude modulate a 1000 kHz sine wave carrier.
The information contained in the time code is seconds through day-of-year coded in Binary Coded
Decimal (BCD). Reference IRIG Document 200-004.
IRIG-B123/003
In addition to the time information identified in B122 above, this format also contains Straight Binary
Seconds (SBS) of day. SBS is provided at the end of the frame, in the 17 bits starting in position 80.
IRIG-B120/000 (IEEE-Standard 1344-1995)
In addition to the time data and the Straight Binary Seconds data this format provides for time/sta-
tus data in the control bit positions of IRIG-B. The information provided there is defined by IEEE
standard 1344-1995: Unit and Tens of Years, Leap Second, Daylight Saving Time, Local Time Offset,
Time Quality and Parity. The IEEE-1344 table provided below shows each bit position with detailed
information.
NASA-36
NASA-36 bit time code is a 100-bit, pulse width modulated format used to amplitude modulate a
1000 kHz sine wave carrier. The information contained in the time code is seconds, minutes, hours
and days. The format is used by several military ranges. Reference IRIG Document 200-04.
2137
The 2137 code is a 25-bit pulse width modulated format used to amplitude modulate a 1000 kHz sine
wave carrier. The information contained in the time code is seconds, minutes and hours. The format
is used by certain security organizations.
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