Z87200 Datasheet, PDF (40/54 Pages) Zilog, Inc. – Spread-Spectrum Transceiver

Z87200
Spread-Spectrum Transceiver
Zilog
CONTROL REGISTERS (Continued)
Address 4C_H through 53_H:
Data Symbol Code
Addresses 4C_H to 53_H contain the binary Data Symbol PN
code sequence values. The storage capacity, assign-
ments, and operation are similar to that of the Acquisi-
tion/Preamble PN code sequence values. The configura-
tion of the bits stored is as shown in Table 22.
Table 22. Data Symbol Codes
Addr 53_H, Bits 7-0
Code Bits 63-56
••••••••••
••••••••••
Addr 4D_H, Bits 7-0
Code Bits 15-8
Addr 4C_H, Bits 7-0
Code Bits 7-0
Transmit Control Registers
Address 54_H:
Bits 1-0 — Transmitter Overlay Select
The Z87200 incorporates programmable overlay code
generators in both the transmitter and receiver. When en-
abled, the selected transmitter overlay code is subtracted
from the data symbols, one overlay bit per symbol in both
BPSK and QPSK modes. No synchronization is required
since the codes in both the transmitter and the receiver are
automatically synchronized by resetting the code genera-
tors at the start of each burst. The addition of the overlay
codes randomizes the transmitted data sequence to guar-
antee that the spectrum of the transmitted signal will be ad-
equately whitened and will not contain a small number of
spectral lines even when the data itself is not random.
Three transmit and receive overlay codes can be selected,
where they are each maximal length sequences with
lengths of 63, 511 and 1023 symbols. The transmitter
overlay codes are enabled and selected by the settings of
bits 1-0 of address 54_H, as shown in Table 23.
Table 23. Transmitter Overlay Code Select
Bits 1-0 in
Addr. 54_H
0
1
2
3
Overlay Code Length
and Polynomial
Overlay Code Disabled
63: 1+x^-2+x^-3+x^-5+x^-6
511: 1+x^-2+x^-3+x^-5+x^-9
1023: 1+x^-2+x^-3+x^-5+x^-10
Bit 2 —Transmitter Symbols Per Burst Off
Bit 2 of address 54_H is not used and must always be set
low (0).
Address 55_H through 56_H:
Transmitter Data Symbols per Burst (bits 15-0)
The data stored as two bytes in addresses 55_H (LS byte)
and 56_H (MS byte) defines the number of data symbols per
burst for the transmitter. This unsigned value must range
from 1 to 65,535 (0001_H to FFFF_H), and the number of
data symbols per burst will be this value plus 1. Note that
the range is slightly different from that in the receiver. Once
the number of transmitted data symbols exceeds this num-
ber, the burst is assumed to have ended and the transmit-
ter is immediately turned off. If the data value is set to
0000_H, then the symbols per burst counter is disabled, per-
mitting the Z87200 to be used for continuous transmission
of data.
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DS96WRL0400