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What does RS232/RS422/V.35 mean?

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Advanced Member level 4
Apr 12, 2005
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convert rs422 to rs232 pinouts

RS422 / V.35 / RS232 selectable interface with 25 pin EIA530 DCE & 37 pin RS449 DCE connectors

Quoted from a requirement of certain project i have to make. What can I extract from it?

What should i get and know to have these interfaces to certain system such as an FPGA based modem?

If anyone dealt before with such serial interface standards, please guide me.. where to start?

Taking RS422 as an example, what should I design for? it contains (as i think) of Tx pin, Rx pin, and some other control pins, right? i think that i should have them all connected, buffered, and configured as I/O/IOP when interfaced with FPGA, right? From where can i get their connections standards?

Another question, are the 25 pin EIA530 DCE & 37 pin RS449 DCE connectors only dedicated to the above three serial standards, or they're general purpose connectors that i can use with any standard? Please clarify briefly..

Please help me,
Thank you all,

what does rs232 mean

First of all, RS422 pinout is not defined in the standard and any pin out table found for RS422 is non-standard ..
In other words, you can do whatever you like, however, ther are some commonly accepted configurations and following them could be only beneficial ..

In this link:
(also suggested by jzo777n) you will find most of known options ..

rs422 signal pictures

IanP and jzo777n,
Thank you for your contribution :)

IanP, What do u mean by the sentence:
RS422 pinout is not defined in the standard and any pin out table found for RS422 is non-standard
I'm sorry, i couldn't totally get what u mean..
Also, you spoke only abut RS422, what about the rest?

Then, in the link(s) provided above, how to map this on actual FPGA project that requires data to be output on these standards? in other words, what are design parameters there??

Thank you in advance,

rs-422 pinout 37-pin connector

I meant exactly what I said: in the RS422/485 there is no standard pin allocation ..

The FPGA will "see" only Rx and Tx pins but beyond that you will need to add external RS422 drivers that will convert unbalanced Rx and Tx signals to balanced or differential signals ..

Example of transmitter and receiver:
SN75C1167/8 2 x T and 2 x R

Other, and cheaper option, use RS485 transceivers such as MAX485 (LT485, ..) and configure one as receiver and one as transmitter ..

mean rs232

Is the RS485 as same as the RS422 ? I don't know them both in fact..

Also, to clarify it well.. I will state what i understood from the above discussion, and please do correct any mistakes i do.

For the RS232, RS422, V.35 i have to have only Tx and Rx pins in the FPGA side, and may be additional pin(s) to select between them..

I have to use also for each of them its corresponding driver IC (i understood that it'll be single IC for each of the three)

This IC will output the required standard signals..

Then, to connect to the required connector, i will need another IC for every connector to be interfaced with the serial standard IC..

Is that correct?
Thank you all,

v.35 wire requirement

Signal levels in the RS422 and RS485 are the same but RS422 was desiged to connect two devices and uses two twisted pairs: one for transmission and one for reception ..
In RS485 you can connect several devices to 4-wire bus (two twisted pairs - full duplex) or 2-wire bus (one twisted pair - half-duplex) ..
Therefore you can use the same drivers for RS485 in RS-422 application and configure control pins in such a way that they are only a transmitter or a receiver ..
In multidrop RS485 applications RS422 transmitters are useless, although in some cases you can use receivers ..

More pictures and details here:
**broken link removed**

This IC will output the required standard signals..

Correct ..

Then, to connect to the required connector, i will need another IC for every connector to be interfaced with the serial standard IC..

That would be the safest approach ..

what do u mean of rs232

You're speaking only about the RS422, does this mean that your speach is also applicable on the rest?

Also, I have a conflict now! I have to use only one connector of each type, then, how many interface chips will I need?

I drew the figure attached below, please check it, and see if it'll function correct, or i have to change anything regarding interface chips or whatever..

Can you also suggest names of the required interface ICs?

Thank you for your concern.

pines rs232 v35

If you don't use more then one connector at a time you can connect outputs or inputs of the same type of electrical signal to more than one connector ..
For example, if you use RS-232 standard it can be connected to DB-9 and DB-25 and you still can use just one set of drivers for both .. see:

As drivers you may consider the following readily available ICs:
Unbalanced -
RS-232: MAX-232, MAX-202, ST-232 or similar ..
Balanced -
RS-422: I would go for RS-485 drivers which have tri-state outputs ..
MAX-485, LTC-485, SN75176, .. or similar ..


rs422 pin out

Here is a user manual of my product which convert RS232 to RS485 directly by hardware. No software, no micro is need for the converting.
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