
P300H
P300 Modem Installation and Operating Handbook
Page 120
Action: 1=Buffer Centre
2=Slip counter reset 3=1:1 Give away control
Action Menu
BER is 100% accurate because as well as counting Errors, the BERT also counts PRBS bits received, and calculates the BER as
<Errors> / <Count of bits received> (ie both are in proportion). This would
not
be the case if we did not count the bits received, and
simply assumed that the error rate was <Errors> / (<Time> x <Rate>).
This may not sit comfortably on first reading, but you are probably happy with the concept that a PRBS multiplexed in with the main data
channel at say 5% of the main data rate will provide the same BER reading as for the main data channel itself. You would probably
agree that the result would be no different if the PRBS content was dropped to say 4% of the main data channel, implying that reducing
the bits available to measure the BER by 20% will have no effect on the validity of the BER reading. The argument for the Internal BERT
is no different, >99.9% of the bits available for BER measurement are used, with the other <0.1% lost as the processor reads the
hardware registers.
6.16
SETUP MENU
See Setup - Initial Configuration Menu on page 51
6.17
ACTION MENU
The options on this menu are fairly self explanatory, however for completeness:
BUFFER
CENTRE
Forces the Rx buffer to re-centre, and will cause a burst of errors. This is
automatically performed when the Rx traffic goes from fail to OK if the option
under
CHANGE, USER-OPT, OPERATION, ACTIONS, BUFFER AUTO CENTRE
is
enabled.
SLIP COUNT
RESET
This resets the counts of underflows and overflows on the
Status
status screens
1:1 GIVE AWAY
When two Modem's are configured as a 1:1 pair, this can be selected on the on-
line unit, to handover control to the off-line unit.