How to configure serial protocol with a start bit

[Nghi Nguyen]

I am using AT-485/4 card to communicate with my device using a specific protocol. The protocol as follow:
+ Full Duplex
+ 19,200 baud rate
+ Character protocol:
- One start bit
- 8 data bit
- One even parity bit
- One stop bit

Labview (v6.0) standard VISA/Serial protocol does not have a start bit. How do I change or make my own VI that can have this capability?

-Nghi Nguyen

[Chris_Rake]

Start bit is automatically generated, there is no way to turn this off or otherwise alter the configuration so the example vis should work for you.

[Nghi Nguyen]

Thank for prompt answer, Chris!

Another question is what is the default signal level for Start/Stop bit? My application needs
-Start bit: low
-Stop bit: high
-Idle : high

I assume this configuration is standard so it will work.

[Chris_Rake]

In UART-based serial communication, idle is always active ("logic high"), start is always inactive ("logic low"), and stop is always active ("logic high"). Again there is no way to configure this, so the default vis should do the trick.

Btw, a word of caution - TX and RX are inverted "on the line" so active (or mark) is a negative voltage and inactive (or space) is a positive voltage. An idle line will have a negative voltage with the start of the data frame being the negative to positive transition that represents the beginning of the start bit.