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COMM status of Fire Alarm connection

Hi.

I'm working on a VB programming project (residing in PC) which needs to receive data from a Fire Alarm 8000 series via RS232 and all the data received need to be converted to MODBUS addresses.

The Fire Alarm 8000 series will not send anything to the RS232 connected to my VB programming unless there's an event like Technical Alarm, fire in a zone, fault and reset. I manage to capture all these different events and convert them to MODBUS protocol addresses respectively.

One of our customer's requirements is that whenever the Fire Alarm 8000 series is disconnected from RS232 port of my PC, my VB program will be able to capture it and set the relevant bit in MODBUS addresses. This can't be done because as i wrote earlier, the fire alarm wont write anything to the RS232 as long as nothing happens. So, disconnecting Fire Alarm 8000 series from my PC is the same as "nothing happens".

Does someone have any idea which my VB program can know when the fire alarm is disconnected from the RS232 port of the PC?

Thanks.

Albert

Reply to
albertleng
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It's years sine I last did anything with RS232 so this is highly speculative: can you make use of any of the other pins/signals on the RS232 connector. Something like DTR (data terminal ready) may have a voltage on it which will disappear if the connection is broken. This is a different approach to using the actual serial data lines themselves.

Peter

Reply to
Peter Amey

i'm using 3 wires to connect to the fire alarm panel. I havent tried to

use the control wires (RTS/CTS). Will that make any difference if i connect also RTS/CTS? I'm not with my fire alarm now. I'll try in a day

or 2.

Thanks.

Reply to
albertleng

In message , dated Fri, 8 Sep 2006, albertleng writes

Do you mean physically disconnected? If so, where can it be physically disconnected? The usual method of doing this is to put an extra pair (or steal a phantom circuit) in the cable, so that you can detect physical disconnection at the PC input.

If you don't mean physical disconnection, you have a much bigger problem. Consult the makers of the fire alarm unit. In many countries, there has to be a provision for monitoring the integrity of the system, so a silent connection is not permitted.

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Reply to
John Woodgate

I meant physically disconnected in which i just disconnect the female RS232 from fire alarm to male RS232 of my PC.

Sorry, what do u mean by

Reply to
albertleng

Only if the device (fire alarm) supports it. The standard protocol is to raise DTR from the PC and the device raises DSR in response. However, many devices don't implement this. Alternatively, you can build a small circuit to detect changes on the RX line, anything non-zero indicates a connected cable.

Reply to
linnix

Are you using any handshaking? From the PC create a loop that sends an RTS, look for the CTS returned. If the PC does not see the CTS create a MsgBox (or whatever) to alarm the RS232 as disconnected.

If not using RTS-CTS then modify the alarm to jump the RTS to the CTS pins. If you can't modify the alarm directly, use an RS232 M to F adapter and create the RTS-CTS loopback in that (they make them so you can wire them as needed).

Reply to
scada

Connecting anything to rts/cts will change nothing on input/output, they were used as handshake signals on modems,etc. , so you can use them to detect a connector , just connect rts/cts at the reciever, and if you change the state of on the output one, you can read the input one. If it does not follow, there is no connection. RTS is output at the computer, CTS is input. DTR and DSR can be used as wel.

Name (V24) 25pin 9pin Dir Full name

----------------------------------------------- TxD 2 3 o Transmit Data RxD 3 2 i Receive Data RTS 4 7 o Request To Send CTS 5 8 i Clear To Send DTR 20 4 o Data Terminal Ready DSR 6 6 i Data Set Ready RI 22 9 i Ring Indicator DCD 8 1 i Data Carrier Detect GND 7 5 - Signal ground - 1 - - Protective ground Don't use this one for signal ground!

Reply to
Sjouke Burry

Hi Sjouke,

Thanks.

I managed to do it with c> albertleng wrote:

Reply to
albertleng

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