Bisync data monitor

Hi,
I am currently working with a unit that transmits serial data in the Bisync format, half duplex, without clock pulses, at 9600bd.
(It is an obsolete Map generator for an ATC radar display.)
I have a need to decipher the data, and don't have access to a costly data monitor.
The data always starts with three 32Hex characters (SYN), followed by the message, all in a continuous bit stream.
The SYN characters are used to synchronise/identify bytes.

Would it be possible to use a PIC to interpret this data?
If so, any suggestions on how it would work?
Obviously, as it is not RS232 (start/stop pulses) that type of data reading cannot be used.

kenmac

kenmac said:

Hi,
I am currently working with a unit that transmits serial data in the Bisync format, half duplex, without clock pulses, at 9600bd.
(It is an obsolete Map generator for an ATC radar display.)
I have a need to decipher the data, and don't have access to a costly data monitor.
The data always starts with three 32Hex characters (SYN), followed by the message, all in a continuous bit stream.
The SYN characters are used to synchronise/identify bytes.

Would it be possible to use a PIC to interpret this data?

Click to expand...

Yes!.

If so, any suggestions on how it would work?

Click to expand...

You first need to work out EXACTLY what the format is, it may be easiest to sit down with a pencil and paper and work it out?.

Obviously, as it is not RS232 (start/stop pulses) that type of data reading cannot be used.

Click to expand...

As there's no seperate clock line then it's an asyncronous format, so it either uses a fixed bit time, with start and stop pulses, like RS232, or it uses a format that includes the clock information within the data - like Manchester coding.

As I said, the signal is definitely Bisync.
The handbook that came with the unit is a translation from French.(Thomson-CSF)
It states "The serial synchronous data signal is transmitted in accordance with symmetrical TTL. The bit clock pulse transitions occur in the middle of the bits".
That can mean the clock pulses are imbedded or it could just mean they occur at that time!
I will have a closer look at the output on a CRO .

kenmac

So much for the handbook info !
I checked the wiring etc and confirmed that it is in fact standard Bisync, complete with separate clock line.
So, that should simplify matters.
Can you point me to any examples of Bisync decoding using a PIC?

kenmac