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Concepts - 2

Line Labels

You can write a program to GOTO or GOSUB to a label instead of a line number. This makes for more readable code.

90 A3 = AIN(0)

100 GOSUB ..FILTER

110 IF FL > 138 THEN GOTO ..OVER_LIMIT

5460 ..FILTER

5470 FL=.875

FL+.125*A3

5480 RETURN

8950 ..OVER_LIMIT

8960 OUT 49,3 :’shut down

Using line labels makes it easier to review code. You would probably know what “F ILTER” does before remembering the

line number it is on.

Line labels must be the first and only information on a line.

NOTE: Labels may not be used with ON GOTO, ON GOSUB, RESTORE, or RESUME.

When labels are used with GOTO, etc., no other statements may follow the label on the same line.

Debugging

CAM BASIC provides you with several methods to help de bug your program. As with all debugging, technique is usu ally

more important than tools. See the Debugging Programs Chapter for more information.

Bit Manipulation

CAMBASIC has commands for manipulating and reading bits. The BIT statement and BIT function can modify and read

individual bits. In order to modify a bit at an I/O port, the port m ust first be r ead, the appropriate bit set and the byte

written back to the port. The BIT statement does this automatically. The BIT function reads back individual bits. It

returns a “ 1” or “ 0” to reflects the state of the bit.

Communications Ports

CAMBASIC supports two serial ports, COM 1 (console) and COM2. Once the serial ports are configured, they can

simultaneously capture data in the background while the program executes. If the ON COM$ statement is used,

CAMBASIC will branch to the user’s routine to handle the incoming data when the message is complete.

Both ports also have output buffering. W hen the PRINT statement is executed, the characters to be printed are sent to the

multitasker and program execution continues at the next statement. The program does not wait until all the characters are

printed. This is especially useful when data is being transmitted at a low baud rate over a modem or radio link. The

output buffers are 255 characters long.

Real time Multitasking

CAM BASIC can perform several kinds of tasks at assembly language speed while the program is running. See the

Multitasking Chapter for more information.

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