| Technote DV 11 | August 1989 |
Changes since October 1989: Corrected syntax errors in the sample code.
Starting with the 128K ROM, we recommend that applications do not check the
low-memory globals SPConfig, PortAUse, and PortBUse
before opening the serial driver. It is no longer the application's
responsibility to test for the availability of the serial ports. When running
AppleTalk Phase 2, it is now possible to use the printer port for asynchronous
serial communication while AppleTalk is active and using an alternate
connection, such as EtherTalk or TokenTalk.
The serial driver automatically verifies that the serial port is correctly configured and free for an asynchronous driver; if it is not correctly configured or free, the serial driver returns either the result code portNotCf or portInUse. The serial driver already has all the code built into it for testing the availability of the serial ports before trying to complete the _Open call. Therefore, since all of the required checks are made inside the driver itself, we recommend that a simple OpenDriver call be made when you need to use a serial port.
By using just the OpenDriver call to the serial driver, you ensure that your code is both user-friendly and compatible with future versions of the System Software.
Pascal
result := OpenDriver('.AOut',AoutRefNumber); {Check result codes in a real application. }
result := OpenDriver('.AIn',AinRefNumber); {See failure mechanism in Sample Code. }
C
result = OpenDriver("\p.AOut",&AoutRefNumber); /*Check result codes in a real app.*/
result = OpenDriver("\p.AIn",&AinRefNumber); /* See failure mechanism in Sample Code.*/
If you must maintain compatibility with the 64K ROMs, call _SysEnvirons, then either call RAMSDOpen for the 64K ROM machines or OpenDriver for the others.