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One questions you can answer in point form sentences, the one question you can answer is RS-232 , now RS-232 to us is an unknown factor,
When he was our age rs-232 was the most important thing in the universe, in the 60’s RS-232 is a modem interface, an interface is, when you have two different technologies working together you require an interface,
Now when he was small computer where new modems were new, they were two different technologies inter-phasing,
The EIA standards groups started the RS-232 interface, first we must know it was bad, it was based on technology in the 60’s which is terrible, but the thing RS-232 its still around, remember 70% people of the world are still using modems, when they go buy this it will say RS-232, even know the
EIA have developed dozens very very good interfaces and RS-232 is still around, RS-232 is a set of instructions that allows computer to talk to its own modem, …..drawing of a computer a
DTE, to a DCE ur computer is attached to a serial cable to your own modem, down the serial cable signals can be sent both ways, the second thing you must know about RS-232 is it was developed in the 60’s data communications was in its infancy and the world was using something,
half duplex transmission an ancient system computer sends data and a computer receive data but not at the same time, modems attached to ur phone data you can transmits and receive data but not at the same time…
…lets look at the interface as it once existed a computer wants to send data, we want to send 0100001 A to another computer the interface working with the os will do the following, find a modem a little thing with a thick cable and if u cut the cable u will see how many wires are inside….when RS-232 was developed, …look at ur serial port even today they still have a serial port in the beginning their was
25 functions…..in a serial cable RS-232 has 25 functions at 25 functions because even though RS-232 can handle Asynchronous trans or Sync transmission, RS-232 is older then PC’s
IBM is in manufacturing PCz, which recognized all PCz will be Asynchronous, if a PC is going to be Asynchronous we don’t need 25 functions we only need 9 functions, RS-232 can do Async and Sync if it’s a = 9 S =25, each wire in the serial cable represents one function, k we want to send the A
INT14 data sends to the UART but the UART cant simply send the data, the UART asks how does it know if its being used by the new computer, first the UART sends a signal down one of the wire in the serial cable
….request to send, RTS pin2 in your serial port if your modem receives your signal in pin2 it know your modem has made a request to send data, what does the modem do, it looks at the phone line if the phone line is idle then the modem sends a signal back to pin 3, pin 3 clear to send….then modem also down the wire a carrier wave, that means the opposing modem cannot send data cause the current modem is sending data, it issues a …….clear to send CTS, then the modem sends the data another little wire in the modem called transmit data, even though RS-232 can have 9 or 25 functions only functions are used for data the remaining functions are all about controlling the data, sends the data down the pins to receive, transmit, send data,
rts cts
Now a modem is a separate device from a computer, when ur grand mama hade a modem she probably had an internal modem, how does the modem know it is turned down, what happens how would the modem know, it knows but the RS-232, one of the functions is used as soon as you turn on a modem the modem sends digital pulses to the computer …..Data Set Ready, DSR, the computer knows its on cause it sends down Data Set Ready, Data set is what we cal it…not modem….the computer now knows its turned one conversely how does the computer know the modem is turned on it does
……Data Terminal Ready, and they can start to communicate,
How many functions we got? 6.
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