TM 11-6625-3041-12/TO 33A1-8-908-1
PR Gen and
The data output from the transmitter is produced by a PR
Single Error
(pseudorandom) Generator. This type of generator produces a
signal that is random enough to approximate real data (real
data is totally random; that is, it is never known whether
the next bit will be a logic 1 or a logic 0) yet repeats
itself in such a manner that a test circuit can determine
whether the received bit is supposed to be a logic 1 or a
logic 0. In the SG-1139 the pattern repeats every 215-1
bits or 32,768-1 = 32,767 bits.
A SINGLE ERROR pushbutton introduces a single error in the
Data Output pattern each time it is pressed.
Error
A second PR Generator is used in the receiver.
It is identi-
cal to the one used in the transmitter and its output is
to the detector is the Data Input from the path under test
via the receiver input circuits. A circuit in the detector
compares the data it is supposed to have (from the second PR
Generator) to that which it is actually receiving from the
input circuits. Any difference is an error. The errors are
counted by the Error Counter and displayed on the 7-digit
ERROR display (up to 9,999,999). This counter and the display
are reset to zero when power is first applied, when the proper
data input (and timing, if required) is first applied, or when
the RESET button is pushed.