Release 1.00
ITU Group 3 Fax Modem
for TMS320C5x
by DSP Software Engineering, Inc.

Software Overview

The Group 3 Fax software is an implementation of the ITU (formerly CCITT) Group 3 Fax standard for 
the TMS320C5x.  The Group 3 Fax standard defines a procedure for analog transmission of binary 
images on the General Switched Telephone Network (GSTN). The Group 3 Fax software is composed of 
implementations of four ITU recommendations for fax control and transmission.
The Group 3 Fax software operates on 30-ms frames sampled at 8 kHz. The demodulator processes 240 
sample frames of linear-PCM data and returns either 9 symbols for V.21, 36 symbols for V.27ter at 
2400 bps, 48 symbols for V.27ter at 4800 bps or 72 symbols for V.29 every frame.  The modulator 
processes a buffer of symbols and generates 240 sample frames of linear-PCM data. The modulator and 
the demodulator symbol word size ranges from 1 bit for V.21 at 300 bps to 4 bits for V.29 at 9600 
bps.

Features and Benefits

•	V.29 data pump for transmission of binary-image data at 9600 and 7200 bps
•	T.30 state machine processor for fax transmission control
•	V.27ter data pump for transmission of binary-image data at 4800 and 2400 bps
•	Software automatic gain control
•	V.21 300-bps data pump for pre- and post-document signaling
•	Error Correction Mode (ECM) is available

Processor and System Requirements

•	Devices supported: TMS320C5x
•	Algorithm category: Fax
•	Requirements:
All memory requirements are in units of 16-bit words. The MIPs ratings presented require the listed 
amounts of dual-access RAM, zero-wait-state program and data memory, and a processing frame size of 
240 samples at 8 kHz. All measurements were made using an executable demo built for a third-party 
PC plug-in board.
Function
MIPS
DARAM
Data
Program
Modulate (Half Duplex)
7.5
0.7 k
1.0 k
6.0 k
Demodulate (Half Duplex)
11.1
0.7 k
1.0 k
6.0 k
T.30/T.30 with ECM
2.0/7.5
0.7 k
13.0 k/13.5 k
12.0 k/14.0 k
Total*
13.1/18.6
0.7 k
14.0 k/14.5 k
18.0 k/20.0 k
*   This is a half-duplex modem. Totals reflect worst-case maximum utilization. Modulator and 
Demodulator share program and data memory.

User Functions

The Group 3 Fax implementation consists of a set of C-callable functions that perform modulation, 
demodulation, data pump control, and status reporting. It also includes functions that reflect the 
implementation's object-based interface. The modulator/demodulator interfaces with arrays of 
linear-PCM samples and 1-, 2-, 3-, or 4-bit symbols.
Interface Functions (general form)
XXX_create (...)
Dynamically allocates and initializes data memory for modem
XXX_delete (...)
Frees modem's usage of dynamically-allocated data memory
Group 3 Fax Processing Functions
MOD_modulate (...)
Performs modulation at the data frame rate
DEM_demodulate (...)
Performs demodulation at the data frame rate
T30_originate(...)
Performs T.30 origination handshake procedure
T30_answer(...)
Performs T.30 answer handshake procedure

Availability

•	Source and object code currently available for licensing.

Company Background and Contact Information

DSP Software Engineering, Inc (DSPSE), founded in 1989, is a leading provider of highly-complex 
digital-signal-processing software used in telecommunications and multimedia applications such as 
computer telephony, digital wireless, PSTN, and satellite communications, and videoconferencing.
Contact:	DSP Software Engineering, Inc
		175 Middlesex Turnpike
		Bedford, MA 01730  USA
		(617) 275-3733
		Fax: (617) 275-4323
		e-mail:  info@dspse.com
		www:  http://www.dspnet.com