Transmitter Description
STEL-2176
54
User Manual
The STEL-2176 provides register space for three
different carrier frequencies. The carrier frequency that
will drive the modulator is selected by the TXFCWSEL
1-
0
control pin input signals. A high on the TXNCOLD
input pin causes the registers selected by TXFCWSEL to
drive the NCO at the frequency determined by the
register value.
The NCOÕs frequency is programmable using the NCO
field (Block 2 Registers 08
H
-00
H
). The nine 8-bit
registers at addresses 00
H
through 08
H
are used to store
the three 24-bit frequency control words FCW ÔAÕ, FCW
ÔBÕ and FCW ÔCÕ as shown in Table 48.
The output carrier frequency of the NCO (f
CARR
) will be:
f
=
f
FCW
2
CARR
CLK
.
24
where, f
CLK
is the frequency of the CLK input signal.
The FZSINB field (bit 7 Block 2 Register 2D
H
) controls
the sine component output of the NCO. This can be
used in BPSK to rotate the constellation 45 degrees (to
Ôon axisÕ modulation). For normal operation, it should
be set to one.
Table 48. FCW Selection
FCW Value Bits
TXFCWSEL
1-0
FCW Selected
23 - 16
15 - 8
7 - 0
00
FCW A
Register 02
H
Bits 7 - 0
Register 01
H
Bits 7 - 0
Register 00
H
Bits 7 - 0
01
FCW B
Register 05
H
Bits 7 - 0
Register 04
H
Bits 7 - 0
Register 03
H
Bits 7 - 0
10
FCW C
Register 08
H
Bits 7 - 0
Register 07
H
Bits 7 - 0
Register 06
H
Bits 7 - 0
11
Zero Frequency
TRANSMIT REGISTER DESCRIPTIONS
Programming the 2176 Transmit and Receive
Functions
The STEL-2176 has a total of xxx registers and they are
arranged as three banks of registers. As indicated in
Table 49, Bank 0 is sub-divided into two groups of
registers which yields a total of four register groups.
Table 49 shows the Bank Address that must be written
to location FF
H
in order to access the respective register
group. The registers comprising The Bank 0 and Bank 1
registers are described in the Receiver Section (see page
20). The registers comprising Bank 2 are described
below. When the Bank 2 (Group 4) registers are
accessed, the hexadecimal register addresses listed in
Table 50 are sent to the Microcontroller Interface (see
page 11) for doing a read or write operation on a
specific register.
Table 49. Addresses of the STEL-2176 Register Groups
Group
Bank
Group Name
Bank Address
(location FF
H
)
1
0
Universal Registers
00
H
2
0
QAM Demodulator Registers Universal Registers
00
H
3
1
Downstream FEC Registers
01
H
4
2
Upstream, or transmitter, Registers
02
H
Block 2, Upstream Registers (Group 4)
Description
Each of the Block 2 registers (see Table 50) is an 8-bit,
Read/Write register and each register contains one or
more data fields, described below. The data fields are
the transmit parameters which control the transmit
characteristics of the STEL-2176. When a transmit
parameter requires more than 8 bits, it is stored in
multiple data fields and stored used two or more
registers.