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V.23 Modem DSP C Code
Description:
implements the ITU Data Modem function V.23. This provides half-duplex
data transmission over 2 wires and full-duplex over 4 wires, at two rates,
one 1200b/s and the other 600b/s, over the telephone network. Also provided
(optionally) is a half-duplex backward channel of 75b/s which can be operated
independently of the main channel. Duplex channel separation is achieved
by band splitting.
The C code is suitable for any
processor with an ANSI-compliant C compiler. It is designed especially
for efficient operation on low-cost fixed-point DSP- and general-purpose
micro-processors. All data memory is specified as 16-bit integer words.
Multiplies are integer 16x16-bit with 32-bit products.
The code is operated by one callable
subroutine for initialisation and one for main-routine processing of input/output
samples and data. The user is responsible for interfacing samples and
data to hardware. The code is re-entrant to facilitate multi-channel operation.
A comprehensive user's guide is provided with the code, together with
example application files. Test results are available. A stripped down
version is available for Caller Identification (CID) use.
Interfaces:
at the sample interface, the code can operate at 8.0kHz and 9.6kHz sample
rates. At the data interface, operation can be in either Asynchronous
or Synchronous mode. In Asynchronous mode, data is transferred with start
& stop bits auto-inserted/-deleted. In Synchronous mode, data is transferred
transparently, with the receiver performing clock recovery on bit transitions.
In both cases, the data can be passed in multiple-bit blocks, and the
nominal clock used is 1200Hz or 600Hz.
At the control interface, the code
has one 16-bit control word to sequence operation and to set operating
parameters such as data size, and one diagnostic word to convey data transfer
status such as ready-to-send and line-signal-detected. With the C code,
control and diagnostics are provided by routine call arguments and returned
values.
Performance:
-
SNR for 10-6 Error Rate on Flat Channel (4kHz BW noise): 1.2kb/s - 12.5dB; 0.6kb/s 8.5dB
Processor Load:
| Sample rate | MIPS# | Data memory (words) | Prog memory (bytes)# |
| 8.0kHz | 4.5( 8.5) | 35(75) | 1.5k(2.7k) |
| 9.6kHz | 5.4(10.2) |
-
#example figures from compiling for the TI TMS320C5000(C55x) DSP processor
- figures in ( ) are with the backwards channel
Availability: NOW - sale is under licence - integration support offered
