Flash duration

I am using Asterisk 1.4 and a 2 FXS + 2 FXO pci card to interface with a legacy pbx and provide auto attendant functionality. An analogue PSTN line is connected to a trunk line interface of the legacy pbx which diverts the incoming line to an analogue extension. The analogue extension is then connected to an Asterisk FXO port. I have configured Asterisk to Flash() the pbx extension and blind transfer to another pbx extension by sending DTMF. This does not work because the pbx hangs up the extension when the Flash() occurs. The problem is that the Dahdi default value for Flash() is 750ms, which is the value used in the USA while I need to configure Dahdi to use the UK value for Flash() of 80ms. I have unsuccessfully worn out Google trying to get clear step by step instructions on how this can be done. Does anybody have any information about how this can be done? I find it strange that this issue is so difficult to pin down.
Thanks for any help.

Most UK PABXes use earth (ground) recall. It is mainly the PSTN that uses timed break. I would expect most PABXes that honoured loop disconnects for recalls would follow the US standards.

Incidentally, pulse dial digit one is usually close enough to UK timed break to work.

If the PABX really does use timed break recall, configs/chan_dahdi.conf.sample fairly clearly documents how to change it.

Even if the PABX is set up for earth recall, which I see no evidence of Asterisk supporting, I imagine it can be reconfigured for the US flash recall.

Sure, I had already inserted 80ms in chan_dahdi.conf but it didn’t seem to have made any difference. I also included threewaycalling=yes and callwaiting=yes, but those did nothing either. Is there some debugging way I can check the flash duration?
I had simulated the conditions using actual pbx extensions and telephone sets with recall buttons and the blind transfer works fine. I then unplugged the sets from the pbx and inserted them in the Asterisk FXO ports and tried the same thing, but the flash is just ignored.

This is the extensions.conf

[incoming]
exten=>s,1,Answer
exten=>s,2,Background(Welcome)
exten=>s,3,WaitExten(5)
exten=>_XXX,1,Set(room=${EXTEN})
exten=>_XXX,2,Wait(1)
exten=>_XXX,3,Flash(80)
exten=>_XXX,4,Wait(3)
exten=>_XXX,5,SendDTMF(${room})
exten=>_XXX,6,Wait(3)
exten=>_XXX,7,Hangup

There is debugging. I have seen the output, but I haven’t used it.

Are you sure the PABX is not expecting earth recall?

Also, dialling a one in pulse mode should be acceptable to a BT type timed break recall system.

The PBX is expecting Timed Break Recall of duration 80mS.

I have tried inserting pulse=yes in chan_dahdi.conf and dialed ‘1’ instead of Flash() but it made no difference. I can’t get Asterisk to pulse dial on the FXO line either.

Any ideas?

Have you tried contacting the vendor of the card? NB Digium support their cards on their commercial web site, not here, although they may say that Asterisk 1.4 is too old.

Yes, that’s the next step I suppose. Thanks for the help.