Abstract: The present invention is an improved data terminal for use in communication and testing of telephone lines which data terminal is operated by a 16-bit microprocessor operating under control of MS-DOS 5.0 program. The data terminal with operating computer and large plurality of telephone test functions is fully contained in a hermetically sealed, lightweight housing to enable easy field handling through data send and receive operations as well as the multiple of telephone line test operations. Power saving aspects of the invention include automatically adjusted LCD backlight control and LCD adjustment caused by large or abrupt temperature changes in the field. The system uses a large microprocessor with EPROM and random access memory with field programmable gating arrays offering virtually thousands of different gate logic decisions.