Apple IIgs #58
Keyboard Modifiers Register Anomaly

Written by Dave Lyons (July 1989)

This Technical Note discusses an anomaly with the keyboard modifiers register at location $C025 which prevents it from always properly reflecting the state of the Control and Shift keys.

There are two cases where pressing the Control key turns on the Shift bit instead of the Control bit in the keyboard modifiers register:

Since the Event Manager reads the modifiers byte, desktop applications may be affected by this anomaly.

Further Reference

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