L64704 LSI Logic Corporation, L64704 Datasheet - Page 208

• Manufacturer Part Number: L64704
• Description: Satellite Decoder Technical Manual 5/97
• Manufacturer: LSI Logic Corporation

Group 4, APR 3 – Set VCR to 0 for rate 1/2, TEI to 0 or 1, TM to 0.
Based on line 8 from
Table
4.2, set PLL_M to 0.
Set Group 4, APR 3 to 0x00.
Group 4, APR 4 – From the graphs starting with
Figure 7.6
on page
page
7-9, choose a value between the in-sync and out of sync curves.
A value of 20% is a reasonable choice for operation at Eb/No of 3.5 and
above. Based on this choice, set VMDC1 to 64 (0x40). This value selects
a window of size 64 x 256 = 16,384 bits.
Set Group 4, APR 4 to 0x40.
Group 4, APR 5-7 – VMDC2 selects a second window. This value con-
trols the window size over which Viterbi Errors are counted. It is used for
calculating the BER, not for the auto-synchronization that is controlled by
6
VMDC1. In this example, choose a window size of 3.932x10
bits =
VMDC2 x 4. Other values may work as well.
Set Group 4, APR 5 to 0x00, set Group 4, APR 6 to 0x00, and set
Group 4, APR 7 to 0x0F.
Group 4, APR 8 – VMBEC is the second parameter that controls the
Viterbi auto-sync. Select a ratio of 20% from the value of
VMDC1 x 256. 0.2 x 16,384 = 3277. Program the value of VMBEC to
(3277 – 32) / 128 = 25 = 0x19.
For lower Eb/No, a ratio of 25% is better. In this case, the calculation is:
0.25 x 16,384 = 4096. So, the value is 32 (0x20).
Set Group 4, APR 8 to 0x20.
Group 4, APR 9 – The DVB sync word is 0x47.
Set Group 4, APR 9 to 0x47.
Group 4, APR 10 – In this example, select a value of 1. See the
description of Group 4, APR 10 on
page
3-33.
Set Group 4, APR 10 to 0x01.
B-20
L64704 Application Notes