AMIS-49587 Datasheet, PDF (13/59 Pages) ON Semiconductor – Power Line Carrier Modem

AMIS−49587
masked ROM. The RAM contains the necessary space to
store the working data. The back−end interface is done
through the Serial Communication Interface block. This
back−end is used for data transmission with the application
micro controller (containing the application layer for
concentrator, power meter, or other functions) and for the
definition of the modem configuration.
Local Port
The controller uses 3 output ports to inform about the
actual status of the PLC communication. IO[0] indicates if
Receiving is in progress and is CRC is OK. TX_ENB is an
output port for the information about the transmitter
enabling. TX_DATA is the output for either the transmitting
data (TX_DATA) or a synchronization signal with the
time−slots (PRE_SLOT).
Serial Communication Interface
The local communication is a half duplex asynchronous
serial link using a receiving input (RxD) and a transmitting
output (TxD). The input port IO[2] is used to manage the
local communication with the base micro (T_REQ) and the
baud rate can be selected depending on the status of two
local input ports (BR_0, BR_1). These two inputs are taken
in account after a AMIS−49587 reset. Thus when the base
micro wants to change the baud rate, it has to set the two
inputs and then provoke a reset.
DETAILED HARDWARE DESCRIPTION
TRANSMITTER PATH DESCRIPTION (S−FSK
MODULATOR)
For the generation of the tones, the direct digital synthesis
of the sine wave frequencies is performed under the control
of the microprocessor. After a signal conditioning step, a
digital to analog conversion is performed. As for the receive
path, a sigma delta modulation technique is used. In the
analog domain, the signal is low pass filtered, in order to
remove the high frequency quantization noise, and passed to
the automatic level controller (ACL) block, where the level
of the transmitted signal can be adjusted. The determination
of the signal level is done through the sense circuitry.
ALC_IN
Transmitter (S−FSK Modulator)
ALC
control
TX_OUT
TX_DATA
TX_ENB
LP
Filter
D/A
Transmit Data
& Sine Synthesizer
ARM
Interface
&
Control
Figure 6. Transmitter Block Diagram
ARM Interface and Control
The interface with the ARM consists in a 8 bit data
register, 2 control registers, a flag defining transmit and
receive and 2 16 bit wide frequency step registers defining
f_M (mark frequency = data 1) and f_S (space frequency = data
0) All these registers are memory mapped.
The transmitter works synchronous with the BIT_CLK
and BYTE_CLK signals when the register TX_RXB in
R_CONF is logic 1. For good operation TX_RXB must
change after an interrupt generated by PRE_BYTE_CLK.
The interface between ARM and transmitter is interrupt
based. At each BYTE_CLK the data from R_TX_DATA is
copied into a buffer register (R_TX_DATA_BUFFER)
The processing of the physical frame (preamble, MAC
address, CRC) is done by the ARM
Sine Wave Generator
A sine wave is generated with a direct digital synthesizer
DDS. The synthesizer generates in transmission mode a sine
wave either for the space frequency (f_S, data 0) or for the
mark frequency (f_M, data1). In reception the synthesizer
generates the sine and cosine waves for the mixing process,
f_SI, f_SQ, f_MI, f_MQ (space and mark signals in phase and
quadrature). The space and mark frequencies are defined in
an individual step 16 bit wide register.
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