Sony Ericsson GR47/GR48 - Manual (Page 52)

7. KEYBOARD INTERFACE
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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
100k
Ω 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.