On Tue, 24 Feb 2004 08:26:59 -0000, you wrote:

>Hi Guys
>I am starting a project where I have to transmit a signal from a HV area
>down to the control unit. and the way that I have to do it is by using =
the
>existing fibre-optics that are already installed from an obsolete system
>previously removed. I do not want to use V/F & F/V converters as that =
was
>not a very good solution in the past, so I am looking into converting =
the
>signal to a 16bit digital signal and then transmit it serially which =
seems
>strait forward enough. The problems are:
>
>        - I would like to use one fibre only if possible
>        - bandwidth needs to be min 100KHz, ideally 200KHz
>        - I need to be able to disconnect the receiver and then connect =
it
>again and automatically synchronize transmission
>        - require error detection i.e. checksum, link failed.
>
>The fibres installed with the fibre-optics TX/RX can do 5MB/s which =
should
>be enough, I do not think I can do it with the PIC as for 200KHz for =
16bits
>you need to be transmitting at around 4MHz. I will be using an ALTERA =
FPGA.
>I can more or less see what to do to transmit the data ( get it into
>digital, feed it to the FPGA as an 16 bit number and then shift it), but=
 the
>automatic synchronization and the error detection is a problem. By
>synchronization I mean if I disconnect the receiver and connect it again=
 and
>it finds it self in the middle of a packet it will wait until it =
receives
>the start of the next one before it considers it a full signal.

You can use a guard interval between bytes or packets. For example if you=
 use a Manchester type
code, this has guaranteed min/max intervals between transitions, and you =
can use intervals in excess
of these for synchronisation. Have a look at the spdif digital audio spec=
 for an example of how to
do this.=20

You may even be able to adapt existing spdif encoder/decoder chips to =
your application.

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