Programming instructions

LIGHT PEN, TYPE 32

The Light Pen is a photosensitive device which detects the presence of

information displayed on a CRT. If the Light Pen is held in front of the CRT

at a point displayed, the Display flag will be set to a 1. The Pen is specified

by 0 and 5 in bits 8 and 9 of the iot instruction. The commands are:

dsf - 700501 - Skip if Display flag is a 1.

dcf - 700502 - Reset the Display flag to a 0.

The Display flag is connected to bit 5 of the iors instruction, and to the

Program Interrupt.

r-l

- (Bit 5)

I I I -

LIGHT

PEN

CONTROL

I I

1 Status Bits:

Figure 11 - Light Pen programming logic

PRECISION CRT DISPLAY, TYPE 300

AND LIGHT PEN, TYPE 32

The Type 30D display plots points at a 20kc rate. The X and Y co-ordinate

buffers (XB and YB) are loaded from the 10 bits, ACsel,.