In serial communication, can you change the start bit to 1 instead of 0?

[GaryZ21]

I am using CVI 7.1 to program the rs485 - 4 port isolation card.  Is it possible to change the start bit value for asynchroneous data?  If so, what would I need to do?  This is for some verifcation testing  I'm performing at work.

[Robert M]

Unfortunately, the value of the start bit is not variable.  This is necessary to adhere to the 485 standard.  Why do you need to change it?  Are you communicating with a device that operates outside the bounds of the 485 standard?

[GaryZ21]

I need to change the start bit value for a qualification testing I'm doing with the 485 card.  So, there is no way?

[Robert M]

There is no way.  If you were to change the start bit value, you would also have to change the idle state value and stop bit value, which would basically be changing the whole protocol.  The value of the start bit is set by the 485 specification and cannot be changed, so I'm curious as to what testing would require this to be changed.

[GaryZ21]

It is just one of the many verification testings I'm performing to see if our units pass or fail based on it's performance specification.

[Robert M]

I'm surprised the performance specification of your device would require you to go outside of the 485 specification.  Is this a specialized device designed to operate on custom serial protocols?

[Henrik_Volkers]

Tests like this are normally performed with a DIO Card (followed by an line driver ) ........