Z87000 Datasheet, PDF (28/50 Pages) Zilog, Inc. – Spread Spectrum Controllers

Z87000/Z87L00
Spread Spectrum Controllers
OPERATION (Continued)
Handset
FRAME_COUNTER
0 12
SYLE timing
Receive data at RX pin
UW_LOCATION-84
Zilog
Figure 7. Frame Counter and UW_LOCATION on Handset
Two modes of search are programmable through the
SYNC_SEARCH_MODE field: “full search” and “window
search”. The full search is used by the handset when first
acquiring the signal from the base station. In full search,
the handset is in receive mode and continuously looks for
a match with the UW. When a match is found and the time
reference established (UW_LOCATION is set), the DSP
processor on the handset detects the synchronization (see
below), switches to Time Division Duplex mode (TDD) and
starts receiving and transmitting alternately. The search
mode should also be switched to “window search” by the
DSP software.
The window search mode only searches for a match in a
certain time window centered around the expected match
time. The window size is programmable by the DSP pro-
cessor in the WINDOW_SIZE field. If the matching does
not occur at the expected time, due to so-called “bit slips”,
the receive frame counter timing is adjusted. Note: al-
though the bit synchronizer is meant to keep track of time
and prevent bit slips when the phone is operating continu-
ously in TDD mode, bit slips are still possible when the
handset is in standby mode, and only receives once in a
while (see description of sleep mode).
SYNC_D Synchronization
When the DSP processor switches the Z87000 operation
to voice mode, the frame synchronization parameters
should be modified by the DSP software to:
s SYNC_SEARCH_MODE = window search
s SYNC_SEARCH_WORD = SYNC_D pattern
In this mode, the receiver searches for the SYNC_D pat-
tern in windows of the incoming data stream. The window
size is determined by the WINDOW_SIZE field.
The transition to voice mode proceeds in two steps,
through an intermediate mode. The mode is set by the
DSP
processor
by
programming
the
MULTIPLEX_SWITCH field. The three modes are:
s SMUX: initial mode. This mode allows acquisition, AFC
operation, UW synchronization and signalling; ADPCM
Processor access disabled; bit inversion disabled.
s STMUX: intermediate mode. This mode allows
SYNC_D frame synchronization and signalling; ADPCM
Processor access disabled; bit inversion enabled.
s TMUX: voice mode. This mode allows voice
transmission, SYNC_D frame synchronization and
signalling; ADPCM Processor access enabled; bit
inversion enabled.
In order to detect synchronizations, the software has ac-
cess to the SYNC_ACQ_IND status field. This field is set
by the Z87000 matching hardware every time a match is
detected within the right time window. The software must
reset the “IND” bit by setting the SYNC_ACQ_CLEAR
field.
In addition, the software can track the frame timing by
reading the frame counter value, available in the
FRAME_COUNTER field. On the base station, where two
frame counters are in use, this field returns the value of the
transmit frame counter.
Every time the frame counter wraps around to 0, a frame
start indicator bit is set (FRAME_START_IND status field).
The software must reset this “IND” bit by setting the
FRAME_START_CLEAR field. If the FS_INT_ENABLE bit
is set, frame starts also trigger interrupts to the DSP pro-
cessor.
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PRELIMINARY
DS96WRL0501