Terminal I/O

[lanmine]

In books,I know in early days,unix hosts could only talk to a device called "teletype",I am in china,so I have no chance to get the point that what is a teletype,maybe printer?
My question is :
Today keyboard devices are connected to unix host through
some interfaces ,monitors(terminal) are connected to unix host through serial ports(local),when I type a letter by pressing a key of keyboard,
some pepole say terminal send the ascii code of the letter to terminal driver ,this procedure is called input of terminal,I could hardly understand that where is the keyboard's use,it seem through the keyboard input that the unix host be notified,how can terminal know the ascii code and send ascii code ?

Forgive my unawareness about unix,thank you.

[Darren Prior]

Hi Richard,

A teletype (short for teletypewriter) is an old type of terminal. They had a keyboard for input and a printer for output (instead of a screen/monitor.)

In the simplest terms a modern terminal will have electronic circuitry that maps a keypress to a particular ascii code. The electronic circuitry will also be able to determine if the shift key is down or the caps lock is on and will map to the upper or lower case character. As an example if I press shift and 'a' the ascii code selected would be 65. Then the ascii code value is converted to a stream of serial data and sent out of the serial port of the terminal. At the other end of the serial cable the serial data stream is decoded to the ascii value and the software of the server decides what to do with it.

If you want to learn more about terminals you should check out information on serial communication and RS232.

hope this helps,

regards,

Darren.

[lanmine]

Thank you Darren.I have thought monitor(CRT) as the terminal .from your reply I know I am wrong .

Can you give me more information about the terminal's defination in unix system(enviroment).

[lanmine]

In addtion,I am Richard,lanmine and I are the same ,only because one day I can not login with lanmine ,so just applied a new one.

Now lanmine can login but Richard can not .

[harry d brown jr]

The first machine I worked on was through a teletype 33:

http://drake.nl/computermuseum/terminals/teletype.html

Make sure to visit the other links.

CRT:
http://whatis.techtarget.com/definition/0,,sid9_gci213839,00.html

VDT:
http://whatis.techtarget.com/definition/0,,sid9_gci214143,00.html

unix:
http://whatis.techtarget.com/definition/0,,sid9_gci213253,00.html


And of course my favorite error message:


Not a typewriter


live free or die
harry

[lanmine]

Thank you harry.You throw me into a huge infomation pool,I like it.I can get what I want.