How can you use a CRT as an alphanumeric display? Discuss with diagram using a ROM and a RAM.

Subject Peripheral and Interfacing
NU Year Set: 2.(c) Marks: 5 Year: 2017

A cathode ray tube display system is provided for displaying alphanumeric characters which are cyclically refreshed in the sequence of selected positions. The system has conventional means for moving the CRT beam through an arbitrary sequence of selected positions with reference to first and second coordinate axes, in response to position signals, and character-defining means for deflecting the beam at each selected position within which a selected character may be defined and in response to signal representations of said selected character for modulating the beam intensity along said pattern to define the character.
The system further includes storage means for sequentially storing a coded representation of the character selected to be displayed as well as tab codes and carriage return codes for said displayed characters.
In addition, the means for generating said position signals include:
(1) means responsive to an access tab code for calculating the tab position for the next character to be displayed with respect to the first coordinate axes only in the initial cycle during which each of the selected characters is formed,
(2) means for storing each of these calculated tab positions, and
(3) means operable only during refresh cycle responsive to a tab code for accessing the stored previously calculated tab position corresponding to said code.

RAM is the memory available for the operating system, programs and processes to use when the computer is running. ROM is the memory that comes with your computer that is pre-written to hold the instructions for booting-up the computer. RAMrequires a flow of electricity to retain data (e.g. the computer powered on).


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