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7. Keyboard Interface
7.1 IO#/KEYROW#
7.2 KEYCOL#
LZT 123 7589 R1A
7. KEYBOARD INTERFACE
To increase I/O capabilities, the radio device optimises the I/O by
multiplexing or sharing different features on single pins. The I/O has been
extended to allow simple interfacing of a matrix keypad.
When configured for keypad operation the software will configure the dig-
ital I/O pins as input or high impedance tri-state. In this state, the keypad
matrix row can be read from the KEYROW# inputs. These pins have a
100k pull-up to 2.75V and the rows are considered activated when the
voltage is pulled low by the external keypad switches.
The keypad matrix column drivers share functionality with the RS232
hardware flow control signals.
In addition to the keypad column outputs it is possible to use a direct
ground connection as an additional column driver, which is interpreted as
column zero.
Simply connect one keypad column directly to ground. When a key in this
column is depressed KEYROW# is activated.
Thus it is possible to create a variety of keypad matrix sizes from single
column to five columns wide.
Finally, a standard keypad matrix directly connects the rows to the
columns whenever a key is depressed. In order to avoid short circuits if
multiple keys are pressed simultaneously, the column drivers must be
open-collector. This must be achieved with external transistors as the logic
drive from the radio device is rail-to-rail. Suitable transistors for this
interface are of the type with built in bias resistors between base and
emitter.
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