MT312C ZARLINK [Zarlink Semiconductor Inc], MT312C Datasheet - Page 12

• Manufacturer Part Number: MT312C
• Description: Satellite Channel Decoder
• Manufacturer: ZARLINK [Zarlink Semiconductor Inc]

MT312
Figure 5 shows the bit errors rising until the
maximum programmed value of VIT ERRPER[23:0]
is reached, when an interrupt is generated on the
IRQ line to advise the host microprocessor that a
new value of bit error count has been loaded into the
VIT ERRCNT [23:0] register. The IRQ line will go
high when the IE FEC register is read by the host
microprocessor. The error count may be expressed
as a ratio:
1.4.1.2 Viterbi Error Count Coarse Indication
To assist in the process of aligning the receiver dish
aerial, a coarse indication of the number of bit errors
being received can be provided by monitoring the
STATUS line with the following set up conditions.
The frequency of the output waveform will be a
function of the bit error count (triggering the
12
--------------------------------------------------------- -
VIT_ERRPER[23:0]*4
VIT_ERRCNT[23:0]
Functional Overview
COURSE
VITERBI
ERROR
COUNT
IRQ
ERROR
COUNT
STATUS
BIT
0
Figure 6 - Viterbi error count coarse indication
0
0
Figure 5 - Viterbi error count measurement
0
VIT_ERRCNT[23:0]
maximum
MAXERR[7:0] register and the dish alignment on the
satellite. This VIT MAXERR mode is enabled by
setting the FEC STAT EN register bit B0. Figure 5
above shows the bit errors rising to the maximum
value programmed and triggering a change of state
on the STATUS line.
1.4.2 The Frame Alignment Block
The frame alignment algorithm detects a sequence
of correctly spaced synchronising bytes in the Viterbi
decoded bit-stream and arranges the input into
blocks of data bytes. Each block consists of 204
bytes for DVB and 147 bytes for DSS. In the DSS
mode, the synchronising byte is removed from the
data stream, so only 146 bytes of a block are passed
to the next stage. The frame alignment block also
removes the 180° phase ambiguity not removed by
Viterbi decoder.
VIT_ERRPER[23:0]
value
VIT_MAXERR[7:0]
programmed
DATA BITS
DATA BITS
into
the
VIT