# 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 = 0 | If PEN was down since last poll, returns -1; if not, returns 0.
n = 1 | Returns 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 = 2 | Returns the y-pixel coordinate when PEN was last activated. The range is within 0 to 199.
n = 3 | Returns the current PEN switch value. Returns -1 if down; 0 if up.
n = 4 | Returns 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 = 5 | Returns the last known valid y-pixel coordinate. The range is within 0 to 199.
n = 6 | Returns the character row position when PEN was last activated. The range is within 1 to 24.
n = 7 | Returns 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 = 8 | Returns the last known valid character row. The range is within 1 to 24.
n = 9 | Returns 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.