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RS232 Splitter?

S

Shadow Lord

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Hello All,

I was wondering if there ever was something like an RS232 splitter?

My understanding is that serial communication is one to one i.e. one device to one port with one cable. However, I was looking at some RS232 RF modems and based on pictures of DIP switch settings it looks like it is possible to set them up for multipoint broadcast. What I'd like to do is connected a device I have to a terminal (current setup) and an RS232 - LAN bridge SIMULTANEOSLY. Note that the idea would be to have live updates on all points continuously so I could not use a switch. Plus a switch would be impractical because if I was close enough to the system to switch inputs then I would not need the remote LAN access. I would try the RF modem route but they are quite expensive and out of (my) budget for a hobby/lark project.

So does anyone know if a cheap RS232 splitter was ever made?

Thanks.
 
I have a little device from Black Box, somewhere, that has multiple RS232 ports, designed for modem sharing iirc. I've never hooked it up, so couldn't say it it's what you're looking for.

I'm not 100% sure where it is, but I'll keep an eye out for it and report back if I find it.
 
Auto-switching boxes (run several terminals, printers, etc.) from a single RS232C point were common, but that apparently is not what you want.

So, some back-of-the-envelope stuff here...

Multidrop transmission (several receivers and one transmitter) should be a no-brainer, as RS232C (as opposed to current-loop) is a voltage-sensitive signaling method. So you should be able to drop a couple of receivers on the same line without much problem.

Mutlidrop reception (several transmitters and one receiver) is a bit more complicated, as that requires negotiation.

Handshaking is another issue. If your protocol uses hardware (e.g. RTS, CTS) handshaking, there's no standard method for arbitrating those signals.

RS-485 is the real multidrop protocol, but I take it that it's not what you're looking for.
 
To answer my question apparently yes but they are not cheap.


Chuck(G) said:
Auto-switching boxes (run several terminals, printers, etc.) from a single RS232C point were common, but that apparently is not what you want.
Click to expand...

Chuck,

here is exactly what I am trying to achieve: I have a home system w/ a PC Weasel 2000 video card. I currently have the I/O connected to a terminal. I recently got the system setup so that I can use WOL to turn it on and to turn it off using ACPI in DOS. Since I no longer have to be physically at the system to turn it on and off I was thinking about connecting the system to my RS232 <-> LAN bridge so I can access it directly from a terminal program on any system. It would be nice if I could connect the I/O to both terminal and bridge at one time to give me complete flexibility. However, I am not sure how well this would work in a live environment where data would be flowing in both directions....
 
roberttx said:
I have a little device from Black Box, somewhere, that has multiple RS232 ports, designed for modem sharing iirc. I've never hooked it up, so couldn't say it it's what you're looking for.

I'm not 100% sure where it is, but I'll keep an eye out for it and report back if I find it.
Click to expand...

Roberttx,

Is this what you have?
 
As the schematic shows here,
the splitter is a passive device that simply "ORs" lines together. The price is probably such because it's a low-demand marginally-useful device--and suitability for general applications seems to be a matter of tinker-tinker-tinker.

Bottom line is that the thing is basically useful when you have multiple listeners and one talker. The other way, not so much.

The old serial auto-switches might be a better solution. Inmac had a whole range of those.

Could you possibly do a similar thing using a LAN hub?
 
Last edited:
Shadow Lord said:
...here is exactly what I am trying to achieve: I have a home system w/ a PC Weasel 2000 video card. I currently have the I/O connected to a terminal. I recently got the system setup so that I can use WOL to turn it on and to turn it off using ACPI in DOS. Since I no longer have to be physically at the system to turn it on and off I was thinking about connecting the system to my RS232 <-> LAN bridge so I can access it directly from a terminal program on any system. It would be nice if I could connect the I/O to both terminal and bridge at one time to give me complete flexibility. ....
Click to expand...

Get another RS-232 to LAN device and set it up as a client device, and hook your terminal to it, and then you can connect to the other serial to LAN device from either the local terminal or a remote terminal. If you just wanted a passive monitor on the second terminal, just connect the TX data from the PC Weasel to the monitoring terminal.
 
How about this: instead of an off-the-shelf LAN <-> RS-232 adapter, hook it to a *NIX box. Run your terminal as the *NIX box's console terminal. Connect to the PC Weasel 2000 with one of the *NIX box's serial ports. Always use `screen` or `tmux` to run the terminal emulator, that way you can leave the console terminal connected but still SSH or Telnet into the *NIX box and grab the session.

There are lots of little embedded systems that have two serial ports and will happily run Linux or one of the BSDs. You could grab a cheap older Soekris device, something out of the 4500 or 4800 series perhaps, and even have a fanless low-power appliance like device. If desired, you could add a wireless card and avoid a hardwired LAN connection, too. A regular PC would also be fine.

Basically, `tmux` stands for "Terminal MUltipleXer," which sounds exactly like what you want.
 
lowen said:
Get another RS-232 to LAN device and set it up as a client device, and hook your terminal to it, and then you can connect to the other serial to LAN device from either the local terminal or a remote terminal. If you just wanted a passive monitor on the second terminal, just connect the TX data from the PC Weasel to the monitoring terminal.
Click to expand...

Lowen,

I am not sure I follow. How do are you exactly proposing the setup? Am I connecting two bridges together?
 
Chuck(G) said:
The old serial auto-switches might be a better solution. Inmac had a whole range of those.
Click to expand...

Chuck,

Do you mean something like this?


Chuck(G) said:
Could you possibly do a similar thing using a LAN hub?
Click to expand...

Not sure what you mean Chuck.


They also make an intelligent buffered splitter that seems to do the job but that costs ~$230 so definitely out.
 
Yes, like that. The idea was that several terminals could talk to the same computer or modem over a single serial line. These came in two flavors, however. Some were just "dumb" and switched whenever a terminal pressed a key--others were "smart" and required a terminal user to use a character or sequence to request access to the common serial port. I don't know which that one is--it may be both.

Maybe I don't understand your need exactly. Maybe a diagram would help?
 
Back in the 90's we provided lots of the Black Box serial splitters with new systems. The proprietary software was licensed per serial port, and customers would put two or three serial terminals and a serial printer or two in their sales area, all sharing one serial port to the system. This arrangement worked quite well, the only drawback was that Black Box products are very pricey.
 
Shadow Lord said:
Lowen,

I am not sure I follow. How do are you exactly proposing the setup? Am I connecting two bridges together?
Click to expand...

Sorry, I have been known to be a bit terse and assume too much tacit knowledge.....

Terminal connects via RS-232 to a client-mode RS-232-ethernet box.
Client-mode RS-232-ethernet box (old terminology is a 'terminal server') connects to LAN
LAN connects to server-mode RS-232-ethernet box.
Server-mode RS-232-ethernet box connects to PC Weasel.

Now, you can connect, one at a time, either an ethernet-capable machine running an ethernet terminal client (PuTTY or raw telnet) or your terminal, using the client-mode RS-232-ethernet box, to your PC Weasel. It would be one at a time unless your server-mode RS-232-ethernet box allows multiple connections (and some do).

Many RS-232-ethernet boxes, such as the SitePlayer Telnet (an embedded version is $15, a boxed version is a bit more), can be set up through their web interface to be either client or server devices.
 
lowen said:
Sorry, I have been known to be a bit terse and assume too much tacit knowledge.....

Terminal connects via RS-232 to a client-mode RS-232-ethernet box.
Client-mode RS-232-ethernet box (old terminology is a 'terminal server') connects to LAN
LAN connects to server-mode RS-232-ethernet box.
Server-mode RS-232-ethernet box connects to PC Weasel.

Now, you can connect, one at a time, either an ethernet-capable machine running an ethernet terminal client (PuTTY or raw telnet) or your terminal, using the client-mode RS-232-ethernet box, to your PC Weasel. It would be one at a time unless your server-mode RS-232-ethernet box allows multiple connections (and some do).

Many RS-232-ethernet boxes, such as the SitePlayer Telnet (an embedded version is $15, a boxed version is a bit more), can be set up through their web interface to be either client or server devices.
Click to expand...

Lowen,

Okay I am following you now. So basically I am using another RS-232 <-> LAN bridge instead of long serial cable to the terminal. That leaves two questions:

1. How compatible is SitePalyer as a client to my RS-232 <-> LAN bridge server (An Avocent ESP-4)?
2. Where can purchase a boxed version? I went to the SitePlayer web site and they list one US distributor who does not have the boxed version. Just kits...

Thanks.
 
I once wired up a RS232 splitter for a pbx logger. As you noted, you can hook the signal up to 2 ports electrically without issue. In my case I only hooked up the receive on the system doing the logging, but on the other system I hooked up both so I could configure the system.

-J
 
Shadow Lord said:
1. How compatible is SitePalyer as a client to my RS-232 <-> LAN bridge server (An Avocent ESP-4)?
Click to expand...

Unfortunately I can't answer that, as I don't have one of those Avocent devices.

2. Where can purchase a boxed version? I went to the SitePlayer web site and they list one US distributor who does not have the boxed version. Just kits...

Thanks.
Click to expand...

I just used the SitePlayer as an example since I have several that were purchased a few years ago and I have used them in this mode (with each other) before. There are others; you'd want to research the protocol your Avocent uses and try to find something that is compatible.
 
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