Z87200 Datasheet, PDF (33/54 Pages) Zilog, Inc. – Spread-Spectrum Transceiver

Zilog
Z87200
Spread-Spectrum Transceiver
sert missed detect pulses; when set low, normal operation vice will terminate the reception of the current burst with
will be enabled whereby data symbols are automatically the next missed detect and return to acquisition mode to
processed immediately following detection of an Acquisi- await the next burst.
tion/Preamble symbol.
4
When bit 5 is set low, the “missed detect” function operates
Bit 3 — Bypass Max. Power Selector
normally; when set high, this function is disabled, allowing
The Z87200’s receiver acquisition and tracking circuitry in- the device to be operated until the end of the specified data
cludes a function that continuously selects the highest es- burst even when the number of “missed detects” exceeds
timated power level out of the three most recent consecu- the Missed Detects per Burst Threshold.
tive estimated power levels from the PN Matched Filter. As
the contents of the sliding 3-sample window change each
cycle of the baseband sampling clock, a new determina-
tion of the highest power level is made from the current set
of the three most recent power level values. The correlated
I and Q channel values within the 3-sample window corre-
sponding in time to the highest observed power level are
then available to be processed in the demodulator.
Bit 6 — Receiver Symbols Per Burst Off
The data stored in addresses 2E_H and 3A_H defines the
number of data symbols per burst that will be processed by
the receiver. This unsigned value must range from 3 to
65,535 (0003_H to FFFF_H), and the number of data symbols
per burst will be this value minus 2. Once the number of
data symbols processed by the receiver exceeds this num-
ber, the burst is assumed to have ended and the receiver
This function assures that, within any 3-sample period, the will immediately return to acquisition mode.
I and Q channel values corresponding to the highest esti-
mated power level will be selected over the two other pairs
of correlated values even if the estimated power levels of
the other pairs exceed the programmed threshold. The
Maximum Power Selector is used in normal operation of
the Z87200 so that the tracking algorithm discriminates by
estimated power levels rather than exact timing intervals,
When bit 6 is set high, the function is disabled, providing
an option to track data symbols under external control for
bursts of more than 65,533 data symbols or indefinitely for
continuous transmission; when set low, the function will
operate normally as defined by the value stored in ad-
dresses 2E_H and 3A_H.
thereby allowing the receiver to adjust to dynamic changes
of the symbol phase. In cases where specific correlation
values are desired regardless of their associated power
level, bit 3 of address 30_H enables the 3-sample power dis-
criminator to be bypassed, thereby making the outputs of
the PN Matched Filter available directly to the demodula-
tor.
Address 31_H:
Bit 0 — Manual Detect Pulse
This bit provides the user a means to externally generate
symbol timing, bypassing and overriding the internal sym-
bol power estimation and tracking circuitry. This function
may be useful in applications where the dynamic charac-
teristics of the transmission environment require unusual
When this bit is set high, the Maximum Power Selector is adjustments to the symbol timing.
bypassed; when it is set low, the Selector is enabled,
where this is the normal operating mode.
When bit 0 of address 30_H is set high (Manual Detect En-
able) and when RXMDET is low, a rising edge on this bit
Bit 4 — Half Symbol Pulse Off
will generate a detect pulse. The function can also be per-
The Z87200 generates two bit clock pulses per symbol formed by means of the RXMDET input signal. Bit 0 of ad-
when operating in QPSK mode, one at the mid-point of dress 31_H and the RXMDET input are logically ORed to-
each symbol and one at the end of each symbol. These gether so that, when either one is held low, a rising edge
clocks are used by the Output Processor to manage data on the other triggers the manual detect function. The rising
flow.
edge of this bit is synchronized internally so that on the
When this bit is set high, the mid-point pulse is sup-
pressed; when it is set low, the device operates in its nor-
mal mode. This function is primarily used for test purposes
and should not normally be used.
second rising edge of the baseband sampling clock that
follows, the rising edge of bit 0 will transfer the I and Q
channel correlated output values of the PN Matched Filter
to the DPSK Demodulator.
Bit 5 — Missed Detects Per Burst Off
To monitor the quality of the received burst data symbols,
the Symbol Tracking Processor keeps track of the cumu-
lative number of received data symbols per burst whose
estimated correlation power level did not exceed the spec-
ified Data Symbol Threshold value. When the accumulat-
ed number of missed detects equals the Missed Detects
per Burst Threshold value stored in address 2F_H, the de-
Address 32_H:
Bit 0 — Receiver Manual Abort
This bit enables the user to manually force the Z87200 to
cease reception of the present burst of data symbols and
prepare for acquisition of a new burst. This function can be
used to reset the receiver and prepare to receive a priority
transmission signal under precise timing control, giving the
user the ability to control the current state of the receiver
as needed.
DS96WRL0400
4-33