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Monitoring 9 Bit Data

Some systems use the first 8 bits to convey the ASCII character, and the 9th bit to convey some other piece of information, such as the status of a device. On these types of systems, set up Serialtest as follows:

In the Set I/O Configuration window, set the word length to 8 and parity to Space or Mark. Mark corresponds to a bit value of 1 and Space corresponds to a bit value of 0. Set the parity even if your system doesn't use parity for error checking. Set the baud for the appropriate rate and capture your data. When the data is captured, Serialtest will receive the first 8 bits from the serial port as data. The 9th bit will be interpreted by the serial port as the parity bit, and the port will tell Serialtest whether there was a parity error or not (i.e. whether the parity bit matched the value selected in the Set I/O window.) 

In the Review Events window, Serialtest will show the ASCII character in either black or red. Black means that the 9th bit matched the parity selected in the Set I/O Configuration window, and red means that the 9th bit was the opposite value.

Example: Assume that the 9th bit is usually in a Space state (i.e. has a value of 0). Set Serialtest for 8 bit word length and Space parity. Most of the data will show up in black on the Review Events window, but on any byte where the 9th bit is a 1, Serialtest will display the byte in red. In this way you know whether the 9th bit is a 0 or 1 based on the color of the byte.