Abstract: A diagnostic display terminal system for remotely troubleshooting hardware, software and operational malfunctions in a computer over telephone lines includes a user-site diagnostic display terminal assembly and a support-site diagnostic display terminal assembly. Each diagnostic display terminal assembly includes a microprocessor controlled display terminal, a telephone instrument and a split baud rate modem, the modem serving to interface the display terminal and the telephone instrument to a telephone line. The system provides alternate voice and data communication between the user-site and the support-site and permits almost instantaneous change-over between voice and data. The telephone link effectively merges the two display terminals together in that each display terminal can monitor the actions of the other and that each display terminal can run all programs executable at the user-site display terminal.