EMBEDDED APPLICATIONS FCT
2 FCT design
Here an application of a fixed-cellular-terminal (FCT) is
used to illustrate the interfacing of a keypad and I
2
C LCD
to the radio device.
Application Block Diagram (Fixed cellular terminal)
2.1
Keypad
2.1.1
Operation
When the script executes it calls a key-scan routine in an
endless loop. When no key is pressed the key-scan
routine returns the code 0xFF. A key-press is detected
when any one of the KeyRow inputs receives a logic low.
The key-scan routine identifies which KeyColumn driver
was active when the key-press was detected and the
routine provides a return code representing the
combination of row and column.
2.1.2
Set-up
The keypad driver setup uses the function kyc() to define
which rows and columns are activated for the application.
This allows the user to select the most suitable keypad
size and avoids tying up control I/O which would be more
usefully applied elsewhere in the application.
This application example utilizes the full complement of
column drivers and row receivers to provide a 20 key
interface.
LZT 123 8016 R1A
5
