This Technical Note describes a method to make the AppleMouse peripheral card interrupt at a rate other than the default 60 Hz. This method does not work on the Apple IIc or IIGS.
This Technical Note describes a previously undocumented call to the AppleMouse II firmware which allows the user to set the interrupt rate to 50 or 60 Hz. (The default is 60 Hz, which keeps the card-generated VBL interrupts synchronized with the actual VBL rate on standard North American Apples; European Apples use 50 Hz as a standard.)
Note: All other accumulator bits are reserved, and must be set to 0.
Note: This call exists only on the AppleMouse card for the IIe or ][+ and should only be used when you know you are working with a IIe or ][+. A user may configure a IIGS to 50 Hz by holding down the Option key while rebooting. The standard North American Apple IIc will not generate 50 Hz VBL interrupts.
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