Rockwell Automation 57C610 Enhanced Basic Language, AutoMax - Manual (Page 71)

6Ć31
Port B Application Notes
1. Port B requires port allocation and error handling to be handled
by the application tasks.
2. OPEN" the port to set the required port characteristics, then
CLOSE" the port.
3. OPEN" the port for NON_EXCLUSIVE access in each task that
needs access to the port. Use the same device number to open
the port in all tasks.
4. Use INPUT #, PRINT #, GET #, and PUT # statements with the
device number used in the OPEN statement to access port B.
5. StopĆAllĆClear commands and power cycle close all ports. Port
characteristics are set to the OS default; the user must set the
port to the required characteristics.
6. Stopping a task does not change the port setup and baud rate.
7. Stopping a task that has EXCLUSIVE access to the port closes
the port on the Processor.
8. Stopping a task that has NON_EXCLUSIVE access only disables
access to the port for the task that was stopped. The other tasks
referencing the port can still transmit or receive data.
9. The operating system does not deĆallocate the port (make the
port available for EXCLUSIVE access) until all tasks referencing
the port have closed the port.
10. Port errors logged to task information (for example, Framing,
Overrun, etc.) will close the port that logged the error.
11. If the port is closed via CLOSE or error, then port statements
PRINT, INPUT, PUT and GET will fail. They will log a Port Not
Open (properly)" error message and abort the operation. No
data will be sent for PRINT and PUT. INPUT and GET will not
suspend the task but will proceed to the next statement on the
current line or next line number. INPUT:EMPTY= and
GET:EMPTY= will not branch to the specified EMPTY line
number, but will operate like the INPUT and GET statements
described above.
Programming Example
The following example uses two tasks on the processor to transmit
and receive data from port B. Software interlocking must be added
to each task attempting to allocate the port to ensure that the tasks
can determine whether the port setup and baud rate have been
initialized prior to opening the port for NON_EXCLUSIVE access.
KYBD.BAS sets the characteristics for port B, closes the port,
reĆopens the port for NON_EXCLUSIVE access, and then sets the
software interlocking flag KYBD_RDY@ TRUE so that DISPLAY.BAS
can open the port for NON_EXCLUSIVE access.
If USERNAME$ is blank, KYBD.BAS prompts the user to enter his
name. DISPLAY.BAS displays the Hello World" message and the
user name if USERNAME$ is not blank. Because the port must be
opened by each task that needs access to the port, the logical
device number used in the OPEN statement must be used with the
INPUT, PRINT, GET or PUT statements.