RE: Serial protocol questions

["Neil Wrightson" <neilw@xxxxxxxxxx>]

Hi All,

I have done a lot of comms work in the past, both RS232 and RS485.
RS485 really has to be a polled environment I.e. a master with polled
slaves. I'm only just starting to look at Xpl at this stage and it appears
that the heartbeat is a rather critical aspect to this protocol.
I believe that the RS485 master should be aware of all of it's slaves and
that the master sends a heartbeat to it's master xXPLHAL??) for its self
and
each of its slaves.
Perhaps xPLHAL should advise the master 485 device what slaves it should be
talking to and what there functionality is.

To me part of the question is, should the RS485 network try to emulate xPL
or as suggested just use a proprietary protocol. I already have proprietary
protocols in place so this would be easier.
But,
In my house I do not want to have multiple RS485 networks with separate
proprietary protocols. I will probably end up making most of my own
hardware, but who knows I may wish to buy somebody else's 485 hardware item
I.e. RFID and connect it onto my network. This wont work if we all have
separate 485 protocols.

I think one of the early on questions is, What is the master? Is it part of
xPLHAL I.e. a PC is the master or should there be a separate standalone
master that talks to HAL via another serial connection. If XPLHAL is the
master we need somebody that can handle the 485 comms on the PC I.e. Rx,Tx
and a handshake line.

By the way, I have already interfaced to RFID devices. Most commercially
available RFID devices talk to other equipment via a 26bit weigand
interface.

Regards,

Neil Wrightson.
-----Original Message-----
From: Frank Mc Alinden [mailto:fmcalind@xxxxxxx]
Sent: Sunday, 23 January 2005 8:08 AM
To: ukha_xpl@xxxxxxx
Subject: Re: [ukha_xpl] Serial protocol questions



Hi Ben

No one that im aware of has done any xPL stuff using rs485 and i
have been pondering over the same questions that you are currently asking,
as i have some rfid readers and i intend to have a little xPL rs485
network......

> 1) Should I be implementing xpl on this device via serial?

Can be done ok , but each device must generate hbeats and on a rs485
network
,multiple devices could send hbeats at the same time ..???

> 2) What schema(s) should I be using?

I would assume the control.basic..Sensor.basic could be used here

> 3) Would it be better to create a proprietary protocol and have
> someone write a plug-in interface to xpl?

Yes this is another option and i have done this with my Probe system....
You still have the issue of devices sending data at the same time therefore
getting corrupted messages unless the app polls each device on the network
...???

> 4) What resources are available to use as a reference beside the xpl
> official website.

No rs485 resources that im aware of ....

Frank



----- Original Message -----
From: <ben@xxxxxxx>
To: <ukha_xpl@xxxxxxx>
Sent: Sunday, January 23, 2005 6:24 AM
Subject: [ukha_xpl] Serial protocol questions


>
>
> I am in the midst of a project and was thinking about making the
> device xpl compatible.
> The device is a magnetic card reader (credit card) with and onboard
> relay to open an electrical door lock. The idea is you would swipe a
> credit card this device sends the account number to a host computer
> (via RS-485). The host determines if the account is allowed access
> and opens or denies access appropriately.
> This device is run by a pic microprocessor.
>
> Questions:
>
> 1) Should I be implementing xpl on this device via serial?
> 2) What schema(s) should I be using?
> 3) Would it be better to create a proprietary protocol and have
> someone write a plug-in interface to xpl?
> 4) What resources are available to use as a reference beside the xpl
> official website.
>
> Thanks!
>
>
>
>
>
>
> xPL Links: http://www.xplproject.org.uk <http://www.xplproject.org.uk>
http://www.xplhal.com <http://www.xplhal.com>
http://www.xpl.myby.co.uk <http://www.xpl.myby.co.uk>
> To Post a Message: ukha_xpl@xxxxxxx
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> Yahoo! Groups Links
>
>
>
>
>
>
>



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