Marquette Hellige GmbH
MicroSmart V 2.xx
Page 17
Servicing Instructions 227 470 35 B - 97.12
Keyboard interface
MicroSmart´s keyboard interface comprises a 5x5 matrix, although only a 4x4 matrix is required and
led to the keyboard. This allows 16 keys to be implemented. The keys are polled in cycles. To do
so, bit combinations are written into a buffer module (column) in cycles. An input module (row)
polled in cycles identifies if a key has been pressed (the combination of output pattern and input
pattern allows the pressed key to be determined).
The keyboard interface is located on the top byte of the data bus. The bits D8..D12 are used for the
keyboard (both input and output).
Both the output buffer and the input buffer are selected via a separate chipselect signal (chipselect
signal of the 68332).
The top two bits (D13...D15) of the input buffer are assigned with additional functions:
D13:
Hardware configuration bit (function undetermined) for future extensions
Default: 0
D14:
Battery monitor bit:
D14 = 1 ==> battery voltage < 11.3V
D14 = 0 ==> battery voltage > 11.3V
D15:
Battery monitor bit:
D15 = 1 ==> battery voltage < 10.3V
D15 = 0 ==> battery voltage > 10.3V
In addition to the 16 keys of the 4x4 matrix, the keyboard includes a key for switching the unit on
and off. Due to its special hardware configuration, this key is not integrated in the matrix.
