Basic computer language commands

Basic computer programming language

PEN Statement and Function

Purpose:

To read the light pen.

Syntax:

As a statement:

PEN ON
PEN OFF
PEN STOP 

As a function:

x = PEN(n)

Comments:

PEN ON enables the PEN read function.

PEN OFF disables the PEN read function.

PEN STOP disables trapping. It remembers the event so immediate trapping occurs when PEN ON is executed.

The PEN function is initially off. A PEN ON statement must be executed before any PEN read function calls can be made, or a PEN read function call results in an "Illegal function call" error.

x = PEN(n) reads the light pen coordinates.

x is the numeric variable receiving the PEN value.

n is an integer within the range of 0 to 9.

Light pen coordinates:

n = 0If PEN was down since last poll, returns -1; if not, returns 0.
n = 1Returns the x-pixel coordinate when PEN was last activated. The range is within 0 to 319 for medium resolution; 0 to 639, for high resolution.
n = 2Returns the y-pixel coordinate when PEN was last activated. The range is within 0 to 199.
n = 3Returns the current PEN switch value. Returns -1 if down; 0 if up.
n = 4Returns the last known valid x-pixel coordinate. The range is within 0 to 319 for medium resolution; or 0 to 639 for high resolution.
n = 5Returns the last known valid y-pixel coordinate. The range is within 0 to 199.
n = 6Returns the character row position when PEN was last activated. The range is within 1 to 24.
n = 7Returns the character column position when PEN was last activated. The range is within 1 to 40, or 1 to 80, depending on the screen width.
n = 8Returns the last known valid character row. The range is within 1 to 24.
n = 9Returns the last known valid character column position. The range is within 1 to 40, or 1 to 80, depending on the screen width.

For execution speed improvements, turn the pen off with a PEN OFF statement for those programs not using the light pen.

When the pen is in the border area of the screen, the values returned will be inaccurate.

Examples:

50 PEN ON
60 FOR I=1 to 500
70 X=PEN(0): X1=PEN(3)
80 PRINT X, X1
90 NEXT
100 PEN OFF

This example prints the pen value since the last poll and the current value.

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