Integrator's Manual GR47/GR48

7. KEYBOARD INTERFACE

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.

7.1 IO#/KEYROW#

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

100kΩ pull-up to 2.75V and the rows are considered activated when the

voltage is pulled low by the external keypad switches.

7.2 KEYCOL#

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.