Chapter 2: TI-83 Plus Specific Information 63
TI-83 Plus Developer Guide Third Release May 28, 2002
DRIVERS LAYER
The Drivers layer of the TI-83 Plus system includes such areas as the keyboard, the
display, and the link port.
Keyboard
There are two ways to read key presses on the TI-83 Plus.
– Poll for scan codes directly.
– Use the system key read routine, GetKey.
• Poll for scan codes
This method is used in two different situations.
– When alpha or second functions located on the keyboard are not used in the
application.
– When keys need to be recognized as fast as possible, this is usually used for
game-type applications programming.
– See the Automatic Power Down (APD) section.
This method will allow an application to know what physical key is pressed only.
– This method will not support silent link activity. Any link activity started by
either another unit or a computer will not be detected by the system. Applications
must poll for link activity on their own. See the Link Port section later in this
chapter.
How it works:
– The system interrupt handler will look for key presses and when one is detected,
it will write the scan code for that key to a RAM location. An application will then
periodically check that RAM location for a scan code value.
– Interrupts must be enabled for the system to scan the keyboard in the
background. This system flag must be reset:
indicOnly, (IY + indicFlags)
If this flag is set, then the interrupt handler will not scan the keyboard. This flag
should only be set when the run indicator needs to be seen and no keyboard
inputs are expected. Setting this flag will cause the interrupt service time to be
shortened and overall execution faster.
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