Browse Prior Art Database

Microprocessor Control of Cursor on Display

IP.com Disclosure Number: IPCOM000052640D
Original Publication Date: 1981-Jun-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 2 page(s) / 14K

Publishing Venue

IBM

Related People

Simmons, J: AUTHOR

Abstract

This idea relates to the control of the position of the cursor on a display. It is usually necessary to provide two alternative forms of control, one governing the speed and direction of the movement of the cursor and the other governing the actual position of the cursor. These two forms of control can be provided using a joystick capable of displacement in X and Y directions from a central or neutral position.

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Microprocessor Control of Cursor on Display

This idea relates to the control of the position of the cursor on a display. It is usually necessary to provide two alternative forms of control, one governing the speed and direction of the movement of the cursor and the other governing the actual position of the cursor. These two forms of control can be provided using a joystick capable of displacement in X and Y directions from a central or neutral position.

To control cursor speed and direction of movement the joystick is displaced, and the speed and direction of movement are directly related to the position of the joystick. It is usual for the speed of movement to change in steps as the position of the joystick is changed. This causes difficulties in accurate operation.

To control cursor position the joystick is displaced, and the position of the cursor is directly related to the position of the joystick. For large movements of the cursor this technique is very good. However, for fine positioning on high resolution displays the technique is very difficult to apply.

The idea proposed seeks to avoid all these difficulties by introducing microcode to provide the control of cursor movement and positioning. The control system consists of a joystick, control logic, a microprocessor interface and microcode within a microprocessor.

The joystick produces analog X and Y signals depending on its position. These analog signals are digitized and applied to the microprocessor interface. The X and Y signals are also used in combination with a mask to operate an interrupt clock when the mask indicates that the joystick displacement is greater than a preset minimum. The interrupt clock operates through the microprocessor interface to control the frequency of interruption of the microprocessor to enable the microprocessor to perform other operations.

The interrupt operation only occurs at the end of each complete raster frame scan of the display so that cursor movement only takes place during flyback time.

There are two sets of microcode used alternatively, the first for controlling the speed and direction of movement of the cursor, and the second for controlling the actual position of the cursor. Microcode - Speed and Direction Control

This set of microcode uses the signs and the values of the X and Y signals to look up a table to provide values of FX and FY, respectively.

The code also detects the end of each display frame scan and uses FX a...