Modem Code for
V.22bis (TMS320C5x/'C25)
by ILLICO!

Software Overview

ILLICO is offering digital signal processing software for implementing the CCITT data modem
standard V.22bis. This software modem can replace conventional data modem chip sets in applications
where a general-purpose TMS320C5x/'C25 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 can
provide the analog interface in many applications. Page-oriented internal RAM addressing allows
easy implementation of multiple independent modems in one processor. All available code was created
by ILLICO's staff and can be customized to support special interfaces and special signal-processing
requirements. The target applications for these software modems are data relay in FAX relay
systems, embedded communications, and network control. Application layer features such as dialing,
error correction protocols, and Hayes-type control interface are not included.

Features and Benefits

•	CCITT V.22bis  (2400 bps and 1200 bps).
•	Answer tone and guard-tone classification (option for data relay).
•	Bell 212A  1200 bps.
•	Zero overhead context switching for multiple modems in one processor.
•	Synchronous or Stop/Start  (V.14) data format.
•	Block-oriented I/O to facilitate processor sharing with other applications.
•	Modem code callable with C-language or assembly-language conventions.
•	Diagnostic mean-square-error calculation and eye-pattern support.
•	Receiver interpolation to support fixed sampling rates.
•	Forty-page Interface Specification to aid installation and application creation.
•	Transmit speed tracking by sample interpolation (option for data relay).

Processor and System Requirements

The following values represent the nominal resource usage. The ranges of MIP performance depend on
the level of internal RAM usage.

•	Data RAM per full-duplex channel
384 words internal (3 pages of data variables)
•	 Program memory
6 k  total
•	Per channel MIPs loading (Million Instructions per Second, zero-wait state)
 7.5  MIPs  (±10%)
Variations of the MIP loading depend on the level of internal RAM usage. The number of independent
data channels that can be supported on a single processor with a particular MIP capacity is easily
calculated from these numbers.

Algorithm Verification

Performance measurements and acceptance tests are performed using simultaneous parallel testing
against industry-standard modems. Test impairments are generated by the T.A.S. model 182 Network
Emulator.

Availability

The TMS320 fixed-point 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