Toshiba TC9314F Manual page 37

5. Key Matrix Structure
The key matrix can have one of the following two structures.
(1) Key data loading by software (software scan)
When loading key data by software, use a key matrix with the above structure. This structure
allows up to 32 (4 × 8) keys to be used. The key data can be loaded at high speed. Also, as the
structure has a high resistance in the N channel FETs of pins T0~T7, there is no need to use a diode
to prevent reverse current flow caused by, for example, multiple keys being pressed.
For this method, set to high the key timing output port data (φL37, φL38) for the key line to be
loaded. Then to determine which keys are pressed, load the key input port (φK28) data to memory. At
this timing, set the other key timing output ports to low. If the corresponding key is pressed, the key
input port data are "1"; if not pressed, "0".
Note 38: When executing a wait instruction (in WAIT mode), applying a high level to a key input pin
releases WAIT mode and restarts the CPU.
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TC9314F
2003-07-03