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Download BBC Microcomputer Advanced User Guide
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18.8.2 The cursor end register (R11) This 5 bit write only register sets the cursor end scan line (see diagram). Mode Cursor end 0 8 1 8 2 8 3 9 4 8 5 8 6 9 7 19 18.8.3 Cursor position register (R14 and R15) This 14 bit read/write register stores the current cursor location. It consists of 8 low order (R15) and six high order (R14) bits. 18.9 LIGHT PENS 18.9.1 Light pens in general A typical light pen consists of a small light sensitive device fixed to the end of a pen shaped holder. The sensor picks up the light given out from the monitor screen and sends an electronic signal into the micro. This LPSTB (light pen strobe) signal can be decoded (because the screen is scanned on a raster basis) and the position of the pen head determined 367
