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How USB is different from RS-232

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kdg007

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How different are the USB and RS-232 ?? I know USB D+/D- works on a twisted pair and the speed is really different.I saw a lot of USB-RS232 converters(UM-232R)but i didnt find any converter in reverse.Why is that ,cant we convert the rs-232 data to USB ?
 

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YOu can surely convert rs-232 signal levels to USB signal levels. But definition of USB doesn't end there. It includes a lot of other details about comms protocols, handshakes, clocks, addressing, command/ response structure etc etc. There is no equivalent in rs-232 as such. However you could possibly write a driver for the rs-232 (receive end) which responds to USB protocol & hence make it work. But they would be non-standard.

However in the case of USB to rs-232, the converter itself is a USB device & hence has the protocol capability built in. All it then has to do is Tx & Rx at rs-232 levels.

Get it ?

---------- Post added at 22:21 ---------- Previous post was at 22:20 ----------

YOu can surely convert rs-232 signal levels to USB signal levels. But definition of USB doesn't end there. It includes a lot of other details about comms protocols, handshakes, clocks, addressing, command/ response structure etc etc. There is no equivalent in rs-232 as such. However you could possibly write a driver for the rs-232 (receive end) which responds to USB protocol & hence make it work. But they would be non-standard.

However in the case of USB to rs-232, the converter itself is a USB device & hence has the protocol capability built in. All it then has to do is Tx & Rx at rs-232 levels.

Get it ?
 
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YOu can surely convert rs-232 signal levels to USB signal levels. But definition of USB doesn't end there. It includes a lot of other details about comms protocols, handshakes, clocks, addressing, command/ response structure etc etc. There is no equivalent in rs-232 as such. However you could possibly write a driver for the rs-232 (receive end) which responds to USB protocol & hence make it work. But they would be non-standard.

However in the case of USB to rs-232, the converter itself is a USB device & hence has the protocol capability built in. All it then has to do is Tx & Rx at rs-232 levels.

Get it ?
_______________________________________________________________________________________________________________________________________________


I am trying to think in a signal conversion level.I used UM232r in which is USB to TTL converter.Which has FT232r which does the main job for the signal conversion from USB to TTL.Basically the signal which we give at the input has to be same as the signal we get at the output ,then we can say the data is proper.So i plug this UM232R to a computer (conect Tx to Rx) and run,it works great..Now if i want to get the data from an Rs-232 device to convert to USB ?? will FT232R be useful ? i mean if i use MAX232 chip to level shift then connect to the FT232R ...
https://www.ftdichip.com/Support/Documents/DataSheets/Modules/DS_UM232R.pdf
 

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RS232 vs TTL signals

RS232 vs TTL Signal.PNG
 
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kdg007

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rs-232 has different voltage levels than TTL,MAX-232 helps us to fix that problem cause it convert the RS-232 to TTL. But I looking for a solution or a possible explanation of converting RS-232 - TTL to USB.for example -- Getting USB signal CONVERTING into TTL --> reconverting from TTL to USB ..I used UM-232r connected between two computers(tx/rx) and it worked now i want to connect computer to other USB devices like mouse,printer,scanner....i want to know the problems i have to face and fix.
 
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I am a bit confused here. I read the thread from the beginning and found that no relation exists with RS232. According to UM-232r datasheet the conversion is between USB and UART.
https://www.ftdichip.com/Support/Documents/DataSheets/Modules/DS_UM232R.pdf

But I looking for a solution or a possible explanation of converting RS-232 - TTL to USB.for example -- Getting USB signal CONVERTING into TTL --> reconverting from TTL to USB ..
OK, but where RS232 comes in? If you need to just implement a serial protocol for exchanging raw data between two PC ports, then you could connect them with each other via two FT232r, or you could use a serial to usb cable.

70_1337114266.jpg


or this maybe?
https://electronics-diy.com/electronic_schematic.php?id=565

i want to connect computer to other USB devices like mouse,printer,scanner....i want to know the problems i have to face and fix.
As described in post #2, this is a different story. You have to fully implement USB protocol, not just physical layer.
https://en.wikipedia.org/wiki/Universal_Serial_Bus
https://www.usb.org/developers/devclass_docs/HID1_11.pdf
 
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hmm.. here is the problem given to me.
-->Design a (TTL or RS-232 standards)circuit which can be used to communicate between two devices other than using a USB cable.If you cant please explain why ?
problem.jpg
as you can see ,i have solved the first solution between two computers using UM232R.
for connecting to Mouse i can use UM232r i am guessing.
But i cannot implement the same idea,if i want to do between Computer to Printer.
I started reading about old and the new methods ,and i got confused with the USB procedure compared to RS-232/TTL...hoping to get a solution
 

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Must be RS-232/TTL.... why r u suggesting LAN ?
 

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wire limitation is not mentioned ...so i am assuming number of wires is not an issue.. wat am i missing ? if i manage to design a TTL circuit ,will the signal be the same at the input and the output ? cause i think speed is the problem .i might have to keep a storage device,to store the data from the USB and send to the TTL circuit.Storage will convert the speed limit keeping the signal safe..am i right ? cause no matter what kind circuit i design in TTL (op-amp,transistors) ,the speed is the major problem.
problem.jpg
 

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RS-232 was the defacto serial port for 2 way communication between 2 devices until ethernet for long distance and USB for short distance became default..
Now RS232 is practically obsolete on portable computers ( no serial ports ) and also most new desktop PC's.

That's a pretty good reason why you can't do it. Of couse it could be converted from USB or ethernet or another port, but why would you ever want to?

Of course if you really wanted to setup a 2 way simple communication system, simply get 2 old computers and a cross-over cable and then connect to your really long cable or get a Limited distance Data set (LDDS) as a repeater for the signals.
Since old PC's would use the same Rx and Tx pins, the crossover cable serves the same purpose as a pair of modem's so it was also called a NULL MODEM cable.
They have similar cross-over cables for USB, ethernet and other ports for direct peer to peer connection. Then you need to software to run it.

My favorite auto scripting serial port software was called Q-Modem from MUstang Software in the 70's. It was a great standard tool in the BBS dial-up days.

Other than doing your homework( which I wont) does that answer your question?
 
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kdg007 said:
for connecting to Mouse i can use UM232r i am guessing.

i might have to keep a storage device,to store the data from the USB and send to the TTL circuit.Storage will convert the speed limit keeping the signal safe..am i right ? cause no matter what kind circuit i design in TTL (op-amp,transistors) ,the speed is the major problem.

Please read post's 7 last reference down to the bottom (pdf file). It's on Human Interface Devices (HID). Speed is not the only issue. You can't escape by just sending raw data. You must implement other things as well.
 
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....i might have to keep a storage device,to store the data from the USB and send to the TTL circuit.Storage will convert the speed limit keeping the signal safe..am i right ? cause no matter what kind circuit i design in TTL (op-amp,transistors) ,the speed is the major problem.
View attachment 74286

Using just a storage-device to somehow match speeds is a Baaa..aad idea. Unless you make many assumptions about the duty cycle/ max tx data etc etc (which a good comms channel should NOT), how will you decide how much to store ? For long bursts of data you will run out of space real quick..., and then what ?

Better is to have a small storage, and a good handshake protocol with the sender/ transmitter to start/ stop transmission.
 
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based on post #9 , not the original question. this is all u need 2 do. THe other suggestions are irrelevant because the question did not give the intent or purpose to question. This answer solves his unstated purpose which was later given in post#9
(edited ...tony)
**broken link removed**
 
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based on post 39 , not the original question. this is all u need 2 do.
**broken link removed**
I cannot see how this reference contributes to this discussion. This link describes a procedure on how to establish communication between PC's RS-232 port and a specific CNC's RS-232 port, using a specific software.
 
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Using just a storage-device to somehow match speeds is a Baaa..aad idea. Unless you make many assumptions about the duty cycle/ max tx data etc etc (which a good comms channel should NOT), how will you decide how much to store ? For long bursts of data you will run out of space real quick..., and then what ?

Better is to have a small storage, and a good handshake protocol with the sender/ transmitter to start/ stop transmission.
___
can u suggest any good storage idea ? u mean a microprocessor ?

---------- Post added at 11:26 ---------- Previous post was at 11:24 ----------

RS-232 was the defacto serial port for 2 way communication between 2 devices until ethernet for long distance and USB for short distance became default..
Now RS232 is practically obsolete on portable computers ( no serial ports ) and also most new desktop PC's.

That's a pretty good reason why you can't do it. Of couse it could be converted from USB or ethernet or another port, but why would you ever want to?

Of course if you really wanted to setup a 2 way simple communication system, simply get 2 old computers and a cross-over cable and then connect to your really long cable or get a Limited distance Data set (LDDS) as a repeater for the signals.
Since old PC's would use the same Rx and Tx pins, the crossover cable serves the same purpose as a pair of modem's so it was also called a NULL MODEM cable.
They have similar cross-over cables for USB, ethernet and other ports for direct peer to peer connection. Then you need to software to run it.

My favorite auto scripting serial port software was called Q-Modem from MUstang Software in the 70's. It was a great standard tool in the BBS dial-up days.

Other than doing your homework( which I wont) does that answer your question?

______
yes,i know you can simply do it with two computers with serial communciations,but i want to know the complications of connecting USB -> TTL --TTL back to USB... .... i know its not as simple as sending the signal and getting it back.

---------- Post added at 11:27 ---------- Previous post was at 11:26 ----------

Please read post's 7 last reference down to the bottom (pdf file). It's on Human Interface Devices (HID). Speed is not the only issue. You can't escape by just sending raw data. You must implement other things as well.

Other things like handshaking u mean ?
 

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