MT9072 Datasheet, PDF (90/275 Pages) Zarlink Semiconductor Inc – Octal T1/E1/J1 Framer

MT9072
Data Sheet
14.1.4 T1 Pseudo-Random Bit Sequence (PRBS) Testing
The MT9072 includes both a pseudo random bit sequence (PRBS) generator of type (2¹⁵-1), and a reverse PRBS
generator (decoder), which operates on a bit sequence, and determines if it matches the transmitted PRBS type
(2¹⁵-1). Bits which don’t match are counted by an internal error counter. This provides for powerful system
debugging and testing without additional external hardware.
If control bit ADSEQ (register address Y01) is zero, any transmit (internal DSTi) timeslot or combination of transmit
timeslots may be connected to the PRBS generator. Timeslot n is selected by setting the TTSTn bit in the Timeslot
n Control Register (address Y90-YA7), where n is 0 to 23. Any data sent on DSTi is overwritten on the selected
timeslots before being output to TPOS/TNEG.
Similarly, if control bit ADSEQ is zero, any receive timeslot or combination of receive timeslots may be connected to
the PRBS decoder. Timeslot n is selected by setting the RRSTn bit in the Timeslot n Control Register (register
address Y90-YA7), where n is 0 to 23.
PRBS data is distributed to the transmit channels sequentially one byte at a time. Consequently, the data received
must be in the same order that it was sent, in order for the PRBS decoder to correctly operate on the data.
If one channel is tested at a time, then the PRBS transmit timeslot does not have to match the PRBS receive
timeslot. However, if more than one channel is tested, then the number of transmit timeslots must match the
number of receive timeslots, and the order of the transmit timeslots must match the order of the receive timeslots.
This will ensure that the sequential data bytes received by the PRBS decoder are in the correct order.
Consequently, particular care must be taken when using an external loopback where the channel order may be
reversed, or where the data has passed through a digital switch which doesn’t buffer all channels to the same
degree.
The PRBS decoder must have sufficient data pass through it before it begins to operate correctly, therefore, the
errors generated by the decoder immediately following start-up should be ignored.
If the PRBS testing is performed in an external loop around using Timeslot Control, then both Timeslot Control bits
TTSTn and RRSTn should also be set.
Register
Address
Y01
Y90-YA7
Y15
Y34
Y44
Register
Description
Line Interface and Coding
ADSEQ bit chooses between Milliwatt test sequence and
transmitted PRBS test sequence.
Per Channel Control
If TTST is set for any channel, the test sequence will be
transmitted on that DS1 timeslot. If RRST is set for any channel,
the test sequence will be expected on the receivePCM24 slot.
PRBS Error Counter and CRC The PRBS Error Counter contains error count on the received
Multiframe Counter for PRBS PRBS sequence.
Receive Sync Interrupt Status PRBSOI will indicate an overflow on the PRBS Error Counter.
Receive Sync Interrupt Mask PRBSOIM is the mask for PRBSOI.
Table 44 - Registers Related to PRBS Testing (T1)
90
Zarlink Semiconductor Inc.