CXD1968AR
Interrupts
The INTRPTN pin can be switched active low on the occurrence of one or more of the following conditions:
Receipt of a TPS block
Received TPS parameter change
Receipt of a TPS block with a bad BCH check
Change of AGC lock status
TPS receive frame error
Completion of FFT processing of the current symbol
Occurrence of MPEG2 transport stream lock
Loss of MPEG2 transport stream lock
Occurrence of FEC (sync byte) lock
Occurrence of errored second
Occurrence of severely errored second
Occurrence of more than 8-byte errors in transport stream packet (rejected codeword)
TS smoothing circuit under/overflow
Separate interrupt enable and status bits for each interrupt are provided. An interrupt condition can be latched
without generating INTRPTN to allow interrupt polling.
Diagnostic Interface
There is a diagnostic interface, which enables the following to be read using the I2C interface:
Mean signal-to-noise ratio across all carriers
Signal-to-noise ratio on each carrier
Real and imaginary components of each carrier after channel correction
Real and imaginary components of the channel estimate for each carrier
Estimated noise power for each carrier
BER Measurement
The CXD1968AR FEC includes comprehensive signal quality measurement logic. The current estimated Bit
Error Rate (BER) of the received signal at various points in the receiver and a measure of the long-term signal
quality are both available via I2C registers. It is also possible for a highly accurate BER to be measured, with
a transmitted sequence of NULL MPEG2 packets in accordance with ETSI TR 101 290 v1.2.1. The measurements
available are;
1. Pre-Viterbi decoder BER (can be measured with real live MPEG2 datastreams)
2. Post-Viterbi BER can be measured in two ways:
Using live MPEG2 datastreams. This is an exact measurement provided each transport stream packet
contains no more than 8-byte errors, and is an estimated measurement if the packet contains 8 or more
errors.
Using MPEG2 NULL packets. This is an exact measurement based on comparison between the
received packet and a stored MPEG2-TS NULL packet, and allows more than 8-byte errors in the
received packet to occur without introducing inaccuracies in the BER measurement.
3. Post R/S decoder BER (requires MPEG2-TS NULL packets to be sent)
4. Number of rejected codewords per second (R/S decoder errors due to more than 8-byte errors occurring)
5. Interrupt on occurrence of errored second (ES, at least one rejected codeword/second)
6. Interrupt on occurrence of severely errored second (SES, n or more rejected codewords in a second
where n is a programmable threshold)
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