Toshiba TC9314F Manual page 38

(2) Key data loading by LCD segment output (hardware scan)
Note 39: A key matrix to 4 × 8 = 32 can be created.
Note 40: The same key line cannot contain both push keys and diode jumpers or alternate switches. Place
diode jumpers or alternate switches on the key return signal output side.
When loading key data using the LCD segment outputs, form a key matrix as shown in the
previous diagram. This key matrix requires a diode to prevent reverse current flow. Note the direction
of this diode and the diode jumper.
At the LCD output change timing, the segment pins output the V
loading key data, the segment signal being loaded goes to the V
timing, and the key input pin is pulled down to the GND voltage. If the key is not pressed at this
timing (or there is no jumper diode), the key input pin inputs the GND level. If the key is pressed (or
there is a jumper diode), a voltage equal to the V
is input.
The input data are latched to the key scan data input port (φK38~φK3F) corresponding to the active
LCD segment output line.
If the corresponding key is pressed, the key data are "1"; if not pressed, "0".
Setting the key scan enable bit (φL2FF) to "1" starts the key scan and begins repeated key data
loading.
The time required to load one line of key data is 2 ms. Therefore, load the key scan data
(φK38~φK3F) to data memory while referencing the key scan operating monitor (φK37).
Note 41: The diode jumper data are stored in the latch. Therefore, for efficient use of the data memory
area, you can reference the contents of the latch as required rather than storing the data in data
memory. The contents of the latches are undefined immediately after the CPU restarts after a
CPU stop function shutdown. Accordingly, check that at least one scan data cycle has completed
before using the latch contents.
Note 42: The key scan range is KR
voltage less the drop across one diode ( ∼ − 0.6 V)
LCD
~KR .
0 7
38
(3 V) or GND voltage. When
LCD
voltage at the LCD output change
LCD
2003-07-03
TC9314F