RS232 question..

[notwist]

I am working on a design project involving networking a series of RFID readers. The readers have the RS232 communication interface. I was told that RS232 can only handle a maximum of 2 devices. Is this true? If so, is there any way around this? Thanks.

 

[Blueteeth]

Hmm, as far as I know RS232 is the physical interface, and so only one 'device' per RS232 port.

That said, I believe you can get serial 'hubs' that use addressing to communicate with each device. I do not know how 'electronics savy' you are, but if you are using a PC with two RS232 ports you could use one to select the 'device' and the other for data communication. Or....the first packet you send from the PC the could select the device/address. I guess it depends on how many RS232 devices you need to communicate with, and how fast you wish to do it.

One could use '9' bit communication, with the ninth bit being an adress bit (1 or 0, only two devices) but I doubt your RFID readers use 9 bit comminication.

My two cents,

Blueteeth

 

[Papabravo]

You may connect several receivers to one transmitter. The problem is that you cannot connect many transmitters to a single receiver. Electrically it just won't work. You may be able to find some RS-232 Multiplexers which will help a little bit.

 

[JimB]

As has been pointed out already, RS232 defines an electrical (and mechanical) standard for serial data transmission.
It is only intended for point to point communication, or as you put it "two devices".

If you want to communicate from one master device to several slave devices, one way to go would be to use RS485 rather than RS232.

RS485 is a two wire communication system, when there is no data being transmitted, all devices are in receive mode.
Each slave device has an address (how you organise this is up to you, RS485 only defines the electrical standard, not the message protocol), when the master device (maybe a PC) wants data from a slave device (an RFID reader), it polls the slave and the slave responds with the appropriate message.

Whenever a device (master or slave) wishes to transmit, it has to:
turn on the transmit circuits in the interface,
send the message,
turn the transmitter off and return to recieve mode,
listen for a reply if one is expected.

Have a look at MAX485 (Google it), an IC which implements an RS485 interface.

JimB

 

[notwist]

Thanks guys for the info.

Are there any other alternatives to RS-232? would it be possible to some how "convert" the RS232 output for communication via ethernet?

 

[blueroomelectronics]

An XPORT will convert RS232 to Ethernet.
https://www.lantronix.com/device-networking/embedded-device-servers/xport.html