Z87200 datasheet(40/54 Pages) ZILOG

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Z87200

Spread-Spectrum Transceiver

Zilog

4-40

DS96WRL0400

CONTROL REGISTERS (Continued)

Address 4CH through 53H:

Data Symbol Code

Addresses 4CH to 53H 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.

Transmit Control Registers

Address 54H:

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 54H, as shown in Table 23.

Bit 2 —Transmitter Symbols Per Burst Off

Bit 2 of address 54H is not used and must always be set

low (0).

Address 55H through 56H:

Transmitter Data Symbols per Burst (bits 15-0)

The data stored as two bytes in addresses 55H (LS byte)

and 56H (MS byte) defines the number of data symbols per

burst for the transmitter. This unsigned value must range

from 1 to 65,535 (0001H to FFFFH), 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

0000H, then the symbols per burst counter is disabled, per-

mitting the Z87200 to be used for continuous transmission

of data.

Table 22. Data Symbol Codes

Addr 53H, Bits 7-0

Code Bits 63-56

••••••••••

Addr 4DH, Bits 7-0

Code Bits 15-8

Addr 4CH, Bits 7-0

Code Bits 7-0

Table 23. Transmitter Overlay Code Select

Bits 1-0 in

Addr. 54H

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

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