Meinberg TCR51USB - Manual (Page 9)

9
Functional description
After the received IRIG code has passed a consistency check, the software clock and
the battery backed realtime clock of TCR51USB are synchronized to the external time
reference. If an error in the IRIG telegram is detected, the system clock of the board
switches to holdover mode. Drifting of the internal time base is limited to 1
µsec/sec by
regulating the onboard quartz of TCR51USB. IRIG code includes day of year informa-
tion only. The complete date is kept in the battery backed realtime clock and the software
clock therefore. The received day of year is compared to this complete date once per
minute. If the board detects a difference between received and stored date information,
TCR51USB switches to holdover mode but still synchronizes the internal time base to
the received IRIG code.
The internal system clock is always set to the received IRIG time,
which might have a local offset to UTC. Only if TCR51USB is
configured with this offset, Meinberg driver software is able to set
the system time of the computer correctly.
IRIG telegrams don’t include announcers for the change of time
zone (daylight saving on/off) or for the insertion of a leap second.
Hence the clock will switch into freewheeling mode in case of such
event, and resynchronize afterwards.
The board TCR51USB decodes the following formats:
A133: 1000pps, amplitude modulated sine wave signal, 10 kHz carrier frequency
BCD time of year, SBS time of day
A132: 1000pps, amplitude modulated sine wave signal, 10 kHz carrier frequency
BCD time of year
A003: 1000pps, DC Level Shift pulse width coded, no carrier
BCD time of year, SBS time of day
A002: 1000pps, DC Level Shift pulse width coded, no carrier
BCD time of year
B123: 100pps, amplitude modulated sine wave signal, 1 kHz carrier frequency
BCD time of year, SBS time of day
B122: 100pps, amplitude modulated sine wave signal, 1 kHz carrier frequency
BCD time of year
B003: 100pps,DC Level Shift pulse width coded, no carrier
BCD time of year, SBS time of day
B002: 100pps, DC Level Shift pulse width coded, no carrier
BCD time of year
AFNOR NFS 87-500:100pps, amplitude modulated sine wave signal, 1 kHz carrier frequency
BCD time of year, complete date, SBS time of day
Additional codes are available on request