Rules for the use of Bell Codes

For some time now I've been looking around for the rules about how to use bell codes for block working.
I have found various references in books and on the Web that list the common British bell codes. Most of these give a general description along the line of, "A sends 'Attention' to B. B acknowledges by ringing 'Attention' back. A offers train by ringing appropriate code. B acknowledges by repeating code.'. They then go on to mention codes other than 'Attention' and 'Is line clear for ...'.
What I'm having trouble finding is a clear description of which codes need to be proceeded by 'Attention' and which don't, I assume certain emergency and information codes (e.g. "Train entering section") don't require to be proceeded by 'Attention'.
Similarly what codes don't require acknowledgement by repeating, or might be acknowledged by a different code (which itself must sometimes be repeated by the box that started the exchange). I have seen a mention of 'Restricted Acceptance'.
I ask because I have written a program that can ring and recognise bell codes but I want to build it up with the rules such that it can behave like a Signalman in adjacent box (in computing terms I suppose I should call it "The Chinese Signalbox" :-)

Chris White wrote:
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Have you had a look on these? :-
http://www.signalbox.org /
http://www.home-in-bristol.fsnet.co.uk /

And I should have mentioned trying MERG - Model Railway Electronics Group. Join MERG ( www.merg.org.uk ) for £12 year ( +£3 joining fee), and there's a wealth of information and, more importantly, experience and knowledge amongst the members.

On Sat, 06 Aug 2005 12:26:33 +0100, Dickie mint
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Thanks Dickie but I've been a member for a few years now and have posted the same question to the MERG discussion group :-)

Chris White wrote:
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So you did!
Sorry, I've been a bit behind with checking all my newsgroups and things for a while now, and will be for a while. If I'd checked first I would have noticed!

I think it goes something like this:
a train is to be passed from A to B to C:-
A gives 1 beat to B = attention
B replies with 1 beat
A sends the code for the class of train to B = is line clear for....
if B can accept the train he repeats the code to A and turns his block indicator from line blocked to line clear. A's block indicator shows line clear = permission for train to proceed
if he cannot accept he does not reply, A repeats after a delay
A set signals to clear
As train passes A's box A sends 2 beats to B = train entering section
B put his bolck indicator to train on line A's block indicator shows train on line
B repeats procedure to C
When train passes B he sends train out of section (2 pause 1) to A and sets block indicator to line blocked.
Regards Jeff

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...
Thanks Jeff but that's the basic explanation that I can easily find. What I'm after finding out is which codes and circumstances don't need an 'Attention' before the code plus when the response might be something other than repeating the code back (plus does the other box have to acknowledge such an alternative respone by repeating it back in their due turn?)?

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I couldn't say for sure for all of the bell codes in the book, and they would doubtless have varied by region, area, and over time. Also whatever the rule book might have said, in practice how a signalman worked depended a lot on who his opposite number in the next box was - things were only worked 'to the book' when an inspector was known to be in the area (this was if fact announced by sending a 'dead bell' to the box either side, by pressing and holding the bell key!)
When I used to spend a lot of time in a number of boxes around Northampton in the early '80s, of the everyday codes 'call attention' was only used to precede the offering of a train into section, (including 'shunt into forward section' etc.), and for the opening & closing of box codes - (5-5-5 & 7-5-5 ?). The logic being I suppose, that once a train had been offered the signalman should already be attentive.
I can't think of hearing of any example where the returned code differed from the one sent - the returning of the signal was simply to ensure that it had been received correctly.
HTH, Ian.

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There is more detailed info here: http://www.davros.org/rail/signalling/bellcodes.html
HTH, Ian.

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My information may not be accurate, as it comes from the Great Cockcrow Railway's rulebook (which is modified from a BR one), but this is what it says:
The bell signals that do not require 'Call Attention' are: Train Entering Section Train Approaching Warning Acceptance (see below) Locomotive (or Locomotive & Brake vans) assisting in rear of train. Obstruction danger Train or vehicles running away in right direction (see below)
The situations where a signalman may send back a different code to that received are:
When the signalman has received 'Obstruction Danger' from the box in advance, and is unable to stop a train which has already been accepted by that box, instead of acknowledging 'Obstruction Danger', he should send 'Train or vehicles running away in right direction' instead, without calling attention. The signalman at the box in advance should then take all possible measures to stop the approaching train, and then acknowledge the code.
When a train is accepted under the Warning Arrangement (this is probably the 'Restricted Acceptance' you were thinking of in the original post. The signalman at the box in advance, on receiving the 'Is Line Clear' bell code, responds with the 'Warning Acceptance' code (without calling attention) instead of repeating the 'Is Line Clear'. The signalman at the box in rear should acknowledge the signal, and caution the train accordingly.
My rulebook also suggests that regulations 8 and 9 allow situations where the code sent back is not that received, but these regulations aren't contained in my book (presumably because they are irrelevant to this particular railway). It may, however, be worth looking them up in a proper BR rulebook.
Obviously, the exact details may vary depending on era and region, but I hope helps to give a general idea.