L64777 LSI Logic Corporation, L64777 Datasheet - Page 52

• Manufacturer Part Number: L64777
• Description: DVB Qam Modulator
• Manufacturer: LSI Logic Corporation

2.12.3 Autoacquisition Mode
Figure 2.23 Frequency Acquisition Loop Overview
2-38
runs if ENABLE_NCO_LOOP is 1 (Register 14)
runs if AUTO_ACQUI is 1
step = step + virtual FIFO * nco_gain
reset virtual FIFO
(Registers 38 and 39)
To ease the usage of phase 1, the NCO can use an automatic frequency
acquisition. Enable regulation of the NCO_LOOP_ENABLE (bit 5) and
set the AUTO_ACQUI bit (bit 3) in the NCO control register. Figure 2.23
outlines the parameter usage during automatic frequency acquisition.
Modulator Architecture
init
step = init step (reg 16 to 18)
measurement duration = ref dur (Registers 21, 22)
threshold = reg 43
reset virtual FIFO
threshold = threshold/2 (Register 43)
NCO_GAIN = NCO_GAIN/2 + 1 (Registers 19, 20)
wait until measurement
duration has elapsed
(Register 13, bit 5 = 1)
measurement duration =
2 * measurement duration
abs(virt FIFO)
NCO_GAIN > 1
threshold
below_thres = 1
true
step update indication in
reg 13 will be set and reset
upon read of the register
below_thres = 0
AUTO_ACQUI_RUNNING = 0
false
(Registers 21
and 22)