multi drop network with RS232 interface

[mmohan]

rs232 multi device

Hi,

I am trying multi drop network with RS232 interface. I have a Host (PC) along with three devices. Can any one suggest how can I get single host to multi drop RS232 interface cable.

-MM

 

[juan_jimenezd]

multi-drop rs232 pull-down resistor

My best sugguestion will be to drop RS232 and get in to RS485. If you still need to stay with rs232 then tour best option would be a one way comunication from the PC to your remotes, but no answer back.

 

[pauloynski]

multi-drop networks

It depends if you need half or full-duplex communication. In one case you will need addressable nodes (like RS485). In the other case you will need to develop an arbitration protocol and use compatible drivers (3-state). No one can be reached using simple RS232 drivers unless, as already stated before, you need not to get an answer (all nodes can hear but no one can answer). In both cases you will need a converter (to RS232) box at the PC or master side. When distances are great or if the nodes are not connected to the same power supply it would be wise to opto-isolate them.

 

[FvM]

Re: RS232 multi drop network

I expect that the devices have some addressing capability to assure only one is answering at a time. Some vendors manufacture devices with RS232 interface, that - different from usual devecied - utilizes a tristate driver. They can actually work in a single host multidrop network by simply paralleling all devices. They provide e.g. up to 10 device addresses. Operation is limited to short range, e.g. a laboratory. My customers in the laboratory automation field are using such devices (e.g. VICI mutiposition valve controllers), and they are working quite well to my opinion.

There would be no problem to install a RS485 driver at the device, but then the user needs a special RS485 converter or interface at his PC. It's a kind of poor man's RS485...

Apart from having devices with dedicated hardware, there is an option to simply install 1N4148 diodes in each device's Tx line and a pull-down resistor, at best to a control line at -12V. The solution would be limited due to crosstalk and capacitive load, but is supposed to work as well.