Modem Code for
Group 3 Fax (TMS320C3x)
by ILLICO!

Software Overview

ILLICO is offering TMS320C3x digital signal processing software modules that implement the CCITT 
modem standards for Group 3 FAX: V.21, V.27ter, V.29, and V.17. These software modems can replace 
conventional FAX modem chip sets in applications where a general-purpose TMS320C3x DSP is available 
on a dedicated or shared basis. Digital sample interpolation permits direct "all digital" interface 
with 64-kbps PCM data streams and avoids conversion to an analog signal. For analog environments, a 
simple m- or A-law codec provides the analog interface. Indirect variable addressing allows easy 
implementation of multiple independent modems in one processor.
The target applications for these software modems are FAX relay, interactive voice response 
systems, store-and-forward FAX servers, and multimedia communications. All available code was 
created by ILLICO's staff and can be customized to support special interfaces and special signal 
processing requirements.

Features and Benefits

•	Modem code callable with C-language or assembly-language conventions.
•	Detection of start and end of echo protection tone.
•	HDLC coding for both V.21 and image frames (option).
•	Block-oriented I/O to facilitate processor sharing with other applications.
•	Receiver interpolation to support fixed sampling rates.
•	Diagnostic mean-square-error calculation and eye-pattern support.
•	Detection of V.21 signals in QAM receiver mode.
•	Highly-optimized transmitters for FAX- broadcast applications.
•	Transmit speed tracking by sample interpolation  (option).
•	Forty-page Interface Specification to aid installation and application creation.
•	Zero-overhead context switching for multiple modems in one processor.

Processor and System Requirements

The following values represent the nominal resource usage. To some extent processing time and 
program memory require- ments can be traded off against each other to create other resource mixes. 
The number
of independent FAX channels that can be supported on a single processor with a particular MIPs 
capacity is easily calculated from these numbers.

•	Data RAM per channel
256 words internal (data variable block)
84  words internal or external (equalizer tap block)
200  words external (V.17 only; trellis decoder block)
•	 Program memory
5 k total for V.21, V.27ter, V.29
8 k total for V.21, V.27ter, V.29, and V.17
•	Per channel MIPs loading (Million Instructions per Second, zero wait state)
4.0  MIPs for V.29/V.27ter/V.21 receivers
6.5  MIPs for V.17 receiver

Algorithm Verification

The ILLICO FAX modem code implements all of the features of CCITT Recommendations V.21, V.27ter, 
V.29, and V.17 needed to support Group 3 FAX (CCITT T.4 and T.30). Performance measurements and 
acceptance tests are performed using simultaneous parallel testing against Rockwell modem cards. 
Test impairments are generated by the T.A.S. Model 182 Network Emulator. A demonstration/evaluation 
board with integral test capabilities is available for purchase as part of the software license.

Availability

The TMS320 modem code is available now under a royalty-free licensing arrangement which includes a 
source-code option. Demonstrations are available at ILLICO's offices in Santa Clara, California.

Company Background and Contact Information

ILLICO is a software development and licensing firm specializing in the application of digital 
signal processing to telecommunications product development. We have been active for over seven 
years with U.S. and international clients, principally in the area of voice band modem design. All 
ILLICO products were created by ILLICO's staff and are typically modified to meet special client 
requirements.

Contact:   	Lien Nguyen
		ILLICO!
		2700 Augustine Drive
		Suite 145
		Santa Clara, California  95054
		(408) 980-8179
		Fax: (408) 980-9327