LSI L64777, Technical Manual

Page: 52 / 124

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