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<p align="center"><font size="5"><strong><font color="#400080"><a name="Low Rate Data Modem System Description and Specifications">Low Rate Data
Modem System Description and Specifications</a></font></strong>
</font>
</p>
<p align="left">Click on the links below for detailed information, downloads,
etc.</p>
<p align="left"><font face="Arial"><small><small> <a title="Table listing all AT commands and their meanings" href="#AT_Command_Set_Summary">AT
Commands</a> �
<a title="Block Diagram showing all LRDM components" href="#System_Block_Diagram">Block
Diagram</a>
� </small></small></font><a href="#Command_Handler"><font face="Arial" size="1" color="#0000FF">Command Handler</font></a><font face="Arial"><small><small>
� <a href="#Data Handler">Data Handler</a> �
<a title="Table listing S register equivalents" href="#S_Register_Summary">S Registers</a>
� <a href="#Sequencer">Sequencer</a> �
<a href="download/LRDMUserManual.pdf">User Manual </a></small></small></font></p>
<hr>
<p align="left"><b><font color="#400080" face="Arial" size="4">Overview</font></b></p>
<p align="left">The Low Rate Data Modem System implements a complete low rate
(14,400 bits/sec. and below) data modem system on a DSP chip. It has been developed as a
general purpose DSP replacement for chipset modems that are either inflexible or no
longer available. It's a system framework that is designed to let you mix and match Components to
tailor a modem system that fits your needs and your budget without having to
purchase or store the code for un-needed elements. As an example, you can
build a complete 14,400 bits/sec. modem with v.42 error control and fallbacks to
1,200 bits/sec. using the Low Rate Data Modem System software, and the Data
Bundle (v.32bis, v.22bis, GenDet) and V.42 Components (see <a href="price.htm">price.htm</a>).
Alternatively, if you only needed 2,400 bits/sec. v22bis, then you would only
need to buy the Low Rate Data Modem System software and the v.22bis Object Code
Component. This system would be small enough to fit entirely on-chip on a Texas
Instruments TMS320C5402 or Analog Devices ADSP2185M DSPs with no external RAM.
Since the Low Rate Data Modem System software and the modem components are sold
separately, you can mix-and-match Object Code, Assembly and/or C Source to
balance your cost/code access requirements. </p>
<p><b><font color="#400080" face="Arial" size="4">Key features</font></b>
</p>
<p>
- Complete software solution - just link in the desired Components, boot the code, and make CALL and ANSWER
mode data connections.<br>
- Complete hardware solution requires only:<br>
DSP chip<br>
1 clock oscillator module for DSP and UART baud
clock<br>
1 quad RS-232 level translator (not needed if
interfacing through host port) <br>
Data Access Arrangement (audio codec + phone line
interface) such as Silicon Labs Si3035 .<br>
Boot PROM (not needed if booting through host
interface port)<br>
- V.24 interchange circuits can be brought out to an external register or flag
pins.<br>
- Synchronous data interface built-in<br>
- V.14 async-to-sync converter built-in<br>
- V.42 error control Component option<br>
- V.32bis, V.22bis, V.21, Bell212a, Bell103, Baudot modem Component options.<br>
- CallerID, DTMF detect Component options.<br>
- software UART up to 115,200 bits/sec. through serial port with CTS/RTS flow
control.<br>
- Run-time "baby AT" command set:<br>
ATA, ATD<dialstring>,
ATE<>, ATH, ATM<>, ATN<rate>, ATO, ATZ, A/,
+++<br>
- Compile-time AT S-register configurations.<br>
- Alternate host port command/data interface option.<br>
- Real-time dual-DAC constellation display support.<br>
- Real-time data logging facility.<br>
- <font color="#FF00FF"> Multi-channel</font> ready - you can fit 24 channels (v22bis @ 2,400 bits/sec) on a
single T.I. DSP!<br>
- Audio codec drivers provided for:<br>
AD1847, AD73311, Crystal CS4216, Silicon Labs Si3035, Si3044,
TLC320C44, TLC320AC01, TLC320AD50 <br>
- Entry point provided in scheduler for user function calls with complete
channel memory-access pointer.
</p>
<hr>
<p><font color="#400080" face="Arial" size="4"><b>
<a name="System_Block_Diagram">System
Block Diagram</a></b></font>
</p>
<p>The internal connections, buffers, and function blocks are shown in the block
diagram below:</p>
<p><map name="FPMap0">
<area href="products.htm#UART" coords="82, 88, 159, 146" shape="rect">
<area href="products.htm#UART" coords="82, 361, 158, 417" shape="rect">
<area href="products.htm" shape="rect" coords="532, 88, 618, 147">
<area href="products.htm" shape="rect" coords="533, 362, 617, 423"></map>
<img border="0" src="images/low_rate_block_dia.jpg" usemap="#FPMap0" width="850" height="600">
</p>
<p align="center"><font color="#400080"><strong><big>Low Rate Data Modem System
Block Diagram</big></strong></font></p>
<p><a href="low_rate.htm">Return to Top of Page</a>
</p>
<hr>
<p align="left"><font color="#400080" face="Arial" size="4"><b>
<a name="AT_Command_Set_Summary">AT
Command Set Summary</a></b></font></p>
<p align="left">The Low Rate Data Modem System implements a "baby" AT
command set that implements several industry standard AT commands. These
commands are sent to the system through the software UART from an RS-232
connected terminal device. They allow you to alter the operation of the modem in
real-time.</p>
<div align="left">
<table border="1" cellspacing="1" width="100%">
<tr>
<td width="14%" align="center" bgcolor="#DFE7FF"><b>Command</b></td>
<td width="11%" align="center" bgcolor="#DFE7FF"><b>Response</b></td>
<td width="17%" align="center" bgcolor="#DFE7FF"><b>Function</b></td>
<td width="9%" align="center" bgcolor="#DFE7FF"><b>Default</b></td>
<td width="45%" align="center" bgcolor="#DFE7FF"><b>Parameters/Description</b></td>
</tr>
<tr>
<td width="14%">A/</td>
<td width="11%" align="center">none</td>
<td width="17%">Re-execute command</td>
<td width="9%" align="center">n/a</td>
<td width="45%" align="center">
<p align="left">Forces the system to re-execute the previous command(s).</td>
</tr>
<tr>
<td width="14%">A<n></td>
<td width="11%" align="center">OK</td>
<td width="17%">Auto Answer modes</td>
<td width="9%" align="center">1</td>
<td width="45%" align="left">If the parameter is non-zero, ATA<n> puts the
system in auto-answer mode and answer incoming call after the specified
number of rings are detected. In the special case where "n" is zero
then ATA0 has dual functionality. If auto-answer mode is enabled, then
ATA0 only disables auto-answer mode (analogous to conventional "ATS0=0").
If auto-answer mode is disabled, then ATA0 causes the modem to immediately go
off hook and attempt to connect (analogous to conventional "ATA" command). In this case, the "wait for ringing"
detection is by-passed and the modem immediately starts to generate the
appropriate ANSWER-mode initiation sequence (i.e. it puts out 2100 Hz
ANSWER tone). ATA0 is useful for trunk-based and cellular modes where
there is no audible ring-back associated with call setup.<br>
n=0 <font size="4">�</font> disable auto-answer<b> </b>if auto-answer is
currently enabled<b><br>
</b>n=0 <font size="4">�</font> go off-hook and connect if auto-answer is
currently disabled<br>
<b>n=1 <font size="4">�</font> Auto answer after 1 ring</b></td>
</tr>
<tr>
<td width="14%">B<n></td>
<td width="11%" align="center">OK</td>
<td width="17%">Select ITU/Bellcore mode</td>
<td width="9%" align="center">0</td>
<td width="45%" align="left">Selects between ITU V.22 and Bell212a modem
standards for rate=1200 bits/sec., and between ITU V.21 and Bell103 modem
standard for rate=300 bits/sec. <br>
<b>n=0 <font size="4">�</font> enable ITU (v.22 and v.21) modem mode</b><br>
n=1 <font size="4">�</font> enable Bellcore (Bell212a and Bell103) modem mode</td>
</tr>
<tr>
<td width="14%">C<n></td>
<td width="11%" align="center">OK</td>
<td width="17%">Enable digit detection mode</td>
<td width="9%" align="center">0</td>
<td width="45%" align="left">Enables or disables digit detection (DTMF or
R1) and reporting. If enabled, the system will listen for digits in
parallel with standard modem startup operation. <br>
<b>n=0 <font size="4">�</font> disable digit detection (default)</b><br>
n=1 <font size="4">�</font> enable DTMF digit detection mode<br>
n=2 <font size="4">�</font> enable MF R1 digit detection mode</td>
</tr>
<tr>
<td width="14%">AT</td>
<td width="11%" align="center">OK</td>
<td width="17%">Command line prefix</td>
<td width="9%" align="center">
<p align="center">n/a</td>
<td width="45%" align="left">Attention Code. Precedes all commands except
for the "A/" (repeat command) and "+++" (escape
sequence).</td>
</tr>
<tr>
<td width="14%">D<dial string></td>
<td width="11%" align="center">OK</td>
<td width="17%">DTMF Dial digit string</td>
<td width="9%" align="center">n/a</td>
<td width="45%" align="left">DTMF dial command causes the system to go
off-hook, check for dial tone, and dial the digits specified in <dial
string>. Valid dial string characters are: 0 to 9, A to D, #, *, and
"," (comma=2 sec. pause). In 4-wire mode, used for trunk-based
and cellular
connections, the ATD command can be used with no dial string supplied to
force the modem to go immediately to search for ANSWER from the
responder. This bypasses the wait for billing delay and dial-tone.</td>
</tr>
<tr>
<td width="14%">DT<dial string></td>
<td width="11%" align="center">OK</td>
<td width="17%">DTMF Dial digit string</td>
<td width="9%" align="center">n/a</td>
<td width="45%" align="left">DTMF dial command causes the system to go
off-hook, check for dial tone, and dial the digits specified in <dial
string>. Valid dial string characters are: 0 to 9, A to D, #, *, and
"," (comma=2 sec. pause).</td>
</tr>
<tr>
<td width="14%">E<n></td>
<td width="11%" align="center">OK
<p> </td>
<td width="17%">Terminal Command Echo</td>
<td width="9%" align="center">n=1</td>
<td width="45%" align="left">Terminal Character Echo - enables or disables
echo of characters sent to the modem.<br>
n=0 <font size="4">�</font> disable character echo<br>
<b>n=1 <font size="4">�</font> enable character echo</b></td>
</tr>
<tr>
<td width="14%">H</td>
<td width="11%" align="center">OK
<p> </td>
<td width="17%">Hang Up</td>
<td width="9%" align="center">n/a</td>
<td width="45%" align="left">Hang Up command causes the system to
terminate a call. In v32bis, a "GSTN cleardown" rate pattern is sent, and the
system hangs up within 5 seconds. In v22bis the modem transmits silence
and hangs up immediately.</td>
</tr>
<tr>
<td width="14%">M<n></td>
<td width="11%" align="center">OK</td>
<td width="17%">Data Handler Select </td>
<td width="9%" align="center">n=0</td>
<td width="45%" align="left">Data Handler Select command determines the
type of data processing on the rate data to and from the modem component.<br>
n=0 <font size="4">�</font> V.14 sync-to-async converter - start/stop
bit framing, no error
control<br>
n=1 <font size="4">�</font> synchronous mode - no error control<br>
<b>n=4 <font size="4">�</font> V.42 error control - LAPM protocol</b></td>
</tr>
<tr>
<td width="14%">N<rate></td>
<td width="11%" align="center">OK
<p> </td>
<td width="17%">Modem Bit Rate</td>
<td width="9%" align="center">14,400 </td>
<td width="45%" align="left">Modem Bit Rate command selects the modem data
signaling rate in bits/sec. V.32bis auto-mode fallback to v22bis is
automatically enabled if v.22bis component is available (i.e. built into
the system). Invalid rates are ignored and the rate is unchanged<br>
n=300 <font size="4">�</font> V.21 300 bits/sec.<br>
n=1200 <font size="4">�</font> V.22bis 1,200 bits,sec. <br>
n=2400 <font size="4">�</font> V.22bis 2,400 bits,sec. <br>
n=4800 <font size="4">�</font> V.32bis 4,800 bits,sec. <br>
n=7200 <font size="4">�</font> V.32bis 7,200 bits,sec.<br>
n=9600 <font size="4">�</font> V.32bis 9,600 bits,sec.<br>
n=12000 <font size="4">�</font> V.32bis 12,000 bits,sec.<br>
<b>n=14400 <font size="4">�</font> V.32bis 14,400 bits,sec.</b></td>
</tr>
<tr>
<td width="14%">O</td>
<td width="11%" align="center">OK</td>
<td width="17%">Return to Online </td>
<td width="9%" align="center">n/a</td>
<td width="45%" align="left">Online command causes the data handler to
switch back to the online state and restores the data link. This command
is only effective if the modem is currently connected and is in command
mode as thge result of an escape sequence, +++</td>
</tr>
<tr>
<td width="14%">V<n></td>
<td width="11%" align="center">OK</td>
<td width="17%">Verbose </td>
<td width="9%" align="center">n=1</td>
<td width="45%" align="left">Verbose command causes results to be
displayed in verbose mode (i.e. OK, CONNECT, etc.). Supports standard
modem init strings, and the parameter is currently ignored<br>
<b>n=1 <font size="4">�</font> enable verbose mode</b></td>
</tr>
<tr>
<td width="14%">Z</td>
<td width="11%" align="center">none</td>
<td width="17%">Software Reset </td>
<td width="9%" align="center">n/a</td>
<td width="45%" align="left">Software Reset causes the system to return to
a reset state (on-hook and all command parameters at default).
This command will not echo since it resets the command handler.</td>
</tr>
</table>
</div>
<p align="left"><a href="low_rate.htm">Return to Top of Page</a></p>
<hr>
<p><font size="4" face="Arial" color="#400080"><b><a name="AT_Command_Handler">AT Command Handler</a></b></font>
</p>
<p>The AT Command Handler is separated into transmit and receive (Tx and Rx)
sections operating independently to process AT commands from the user, and pass
command responses and status messages to the user. The Rx-AT Command Handler
section physically monitors the data stream going from the UART to the modem's
transmit data buffer. When in the off-line state, it constantly checks the data
for the presence of the "A" and "T" ascii character
sequence, which signifies the "attention" command from the user. Upon
receipt of these attention characters, the subsequent characters are
evaluated against a list of valid commands and parameters that the Low Rate Data
Modem system responds to. Please see <font face="Arial"><small><small>
<a href="#AT_Command_Set_Summary">AT
Commands</a>
</small></small></font>for a summary table of these commands. If a valid
command is detected, the corresponding LRDM command is issued to the Command
Handler for system evaluation and execution. The Tx-AT Command Handler monitors
the system Command Handler for execution status, and reports "OK" or
"ERROR" messages back to the user indicating either successful
execution or failure to execute the last command. The Tx-AT Command Handler also
echoes all characters back to the user if enabled.
</p>
<p><a href="low_rate.htm">Return to Top of Page</a>
</p>
<hr>
<p><font size="4" face="Arial" color="#400080"><b><a name="Command_Handler">Command Handler</a></b></font>
</p>
<p>The Command Handler is a top-level process that is invoked by the system
framework to interpret system commands and execute them. It includes a function
call from the system scheduler to a command processor, and a circular command
buffer that contains formatted commands. Commands are written to the command
buffer by the AT Command Handler in response to a valid AT command, or directly
by the user via the processor's host port interface, or other memory access
mechanism. Command codes and the command buffer format are specified in the
command.h header file. Some examples of LRDM commands are:
</p>
<ul>
<li>CMD_SOFT_RESET - forces execution of the soft_reset function which
restores the LRDM system to it's initial state. Translated from the ascii
ATZ command.</li>
<li>CMD_HANG_UP - causes the LRDM to hang up the phone line, and return to the
off-line state. Translated from the ascii ATH command.</li>
<li>CMD_AUTOANSWER_CONNECT - causes the LRDM to proceed to connect in ANSWER
mode upon detection of ringing. Translated from ascii ATA command.</li>
</ul>
<p>Commands are formatted with a 3 byte header and optional parameter bytes, and
includes a channel specifier to allow a single command structure to control
multi-channel implementations of the LRDM. In systems where the LRDM is
implemented in a DSP attached to a host processor via a "host port
interface" (please refer to specific DSP devices for HPI), the host can
issue commands to the LRDM via the command buffer, and disable the AT Command
Handler and software UART.
</p>
<p><a href="low_rate.htm">Return to Top of Page</a>
</p>
<hr>
<p><font size="4" face="Arial" color="#400080"><b><a name="Data Handler">Data Handler</a></b></font>
</p>
<p>The Data Handler is a top-level process that is invoked by the system
framework to manage the transmission of actual message data between the line
(i.e. the modem connected to the telephone) and the user interface (i.e. the
UART or direct command interface). Initially the Data Handler is in an
"Idle" state where it simply returns to the caller- no data are
passed. Upon connection to the line, the Data Handler is switched into one of
several possible processing states, and transfers message data. Possible Data
Handler devices include:
</p>
<ul>
<li>Synchronous connection, such as ITU-T V.24, with continuous clock and
data.</li>
<li>Asynchronous start/stop framed using ITU-T V.14 sync-to-async converter.</li>
<li>Asynchronous framed with error control using ITU-T V.42 LAPM protocol.</li>
</ul>
<p>The default condition for the Data Handler is to enable the highest level
device present in the system. If the Low Rate Data Modem has been built with the
v.42 error control component included, then it will be enabled by default and
LAPM will be negotiated immediately upon connection with a remote modem. Bytes
will only be transferred to/from the UART if they are present and error-free in
a data frame. If built with only the v.14 converter present, then only
start/stop bit framing will be provided upon connection with a remote modem.
Again, asynchronous bytes will only be transferred to/from the UART if start bit
has been detected. If the v.24 synchronous interface is included, then the
data stream is passed directly to clock and data pins with no framing or data
processing. Synchronous data are continuously transferred to/from the user I/O
at the channel bit rate regardless of the data contents. </p>
<p><a href="low_rate.htm">Return to Top of Page</a>
</p>
<hr>
<p><font size="4" face="Arial" color="#400080"><b><a name="Sequencer">Sequencer</a></b></font>
</p>
<p>The Sequencer is a top-level process that is invoked by the system framework
to implement the call setup, tear-down, and management state machine. It
consists of a set of functions executing directly from the system scheduler,
that sequence the LRDM through the state processes required to connect to
the phone line and establish a data transfer session with a remote
terminal. The Sequencer is initialized to an "idle" state upon reset,
and always returns to idle upon completion of a call. When the LRDM is commanded
to make a connection (i.e. ATA or ATDT commands), then the Command Handler
forces the Sequencer to transition from "idle" state to an action
state, such as "Seq_wait_for_ring" or "Seq_wait_for_dialtone".
The Sequencer then transitions through the prescribed states required to
establish the data connection and maintain it. Most Sequencer states also
include timeout conditions derived from S-register timeout values that force the
command handler to tear down a call and return to "idle". Sequencer
states contain the "next-state" transition information internally
without access to a soft state table, so users can implement external processing
states by a single state function pointer override.
</p>
<p><a href="low_rate.htm">Return to Top of Page</a>
</p>
<hr>
<p align="left"><font color="#400080" face="Arial" size="4"><b>
<a name="S_Register_Summary">S
Register Summary</a></b></font></p>
<p align="left">The Low Rate Data Modem System implements several of the
industry standard S Register functions in firmware. These registers contain the
default characters and values used by the AT command handler, and since they are
"firmware", they can be modified at compile/assembly time. The table
below summarizes the S Registers available.</p>
<table border="1" cellspacing="1" width="100%">
<tr>
<td width="13%" align="center" bgcolor="#DFE7FF"><b>S Register </b></td>
<td width="18%" align="center" bgcolor="#DFE7FF"><b>Function</b></td>
<td width="9%" align="center" bgcolor="#DFE7FF"><b>Default</b></td>
<td width="40%" align="center" bgcolor="#DFE7FF"><b>Description</b></td>
</tr>
<tr>
<td width="13%" align="center">0</td>
<td width="18%">Rings to answer </td>
<td width="9%" align="left">1</td>
<td width="40%" align="left">Specifies the number of rings required before
the modem will go off-hook after an ATA command has put the system in
Auto-Answer mode.</td>
</tr>
<tr>
<td width="13%" align="center">2</td>
<td width="18%">Escape Characters</td>
<td width="9%" align="left">+++</td>
<td width="40%" align="left">Specifies the character used in the escape
sequence. </td>
</tr>
<tr>
<td width="13%" align="center">3</td>
<td width="18%">Command Terminate Character</td>
<td width="9%" align="left">CR</td>
<td width="40%" align="left">Specifies the character used to terminate a
command string. The default is a carriage return, CR.</td>
</tr>
<tr>
<td width="13%" align="center">4</td>
<td width="18%">Line Feed Character</td>
<td width="9%" align="left">LF</td>
<td width="40%" align="left">Specifies the character used to force a
terminal line-feed. The default is a line feed, LF.</td>
</tr>
<tr>
<td width="13%" align="center">5</td>
<td width="18%">Back Space Character</td>
<td width="9%" align="left">BS</td>
<td width="40%" align="left">Specifies the character used to back the curser
to it's previous position - one position to the left. The default is a
back-space, BS.</td>
</tr>
<tr>
<td width="13%" align="center">6</td>
<td width="18%">Wait Time For dial tone</td>
<td width="9%" align="left">2 Sec.</td>
<td width="40%" align="left">Specifies the timeout for dial tone to be
detected after the system has gone off-hook.</td>
</tr>
<tr>
<td width="13%" align="center">7</td>
<td width="18%">Wait Time For Carrier</td>
<td width="9%" align="left">30 sec.</td>
<td width="40%" align="left">Specifies the timeout for the detection of a
modem carrier after the system has dialed or answered.</td>
</tr>
<tr>
<td width="13%" align="center">8</td>
<td width="18%">DTMF Pause Duration</td>
<td width="9%" align="left">2 sec.</td>
<td width="40%" align="left">Specifies the duration of silence generation
for a dial string pause character, ",". </td>
</tr>
<tr>
<td width="13%" align="center">9</td>
<td width="18%">Carrier Detect Time</td>
<td width="9%" align="left">600 msec.</td>
<td width="40%" align="left">Specifies how long a carrier must be present
for the modem to confirm it's detection, in units of 1/10 sec. </td>
</tr>
<tr>
<td width="13%" align="center">10</td>
<td width="18%">Carrier Loss Time</td>
<td width="9%" align="left">700 msec.</td>
<td width="40%" align="left">Specifies how long a carrier must be absent for
the modem to initiate termination of a call, in units of 1/10 sec.</td>
</tr>
<tr>
<td width="13%" align="center">11</td>
<td width="18%">DTMF Tone Duration</td>
<td width="9%" align="left">63 sec.</td>
<td width="40%" align="left">Specifies the duration of a DTMF digit tone
pair, in units of 1/100 sec</td>
</tr>
<tr>
<td width="13%" align="center">12</td>
<td width="18%">Escape Code Guard Time</td>
<td width="9%" align="left">1.0 sec.</td>
<td width="40%" align="left">Specifies the minimum silence interval
preceding and following an escape sequence (+++), and the maximum gap
between any two consecutive escape characters. Specified in units of 1/50
sec.</td>
</tr>
</table>
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