DS_1215F_003
73S1215F Data Sheet
1.7.12 Keypad Interface
The 73S1215F supports a 30-button (6 row x 5 column) keypad (SPST Mechanical Contact Switches)
interface using 11 dedicated I/O pins.
Figure 12 shows a simplified block diagram of the keypad interface.
KORDERL / H Registers
7
6
5
4
3
2
1
0
7
6
5
4
3
2
1
0
VDD
COL4:0
Keypad Clock
Column Value
Scan
5
7
6
5
4
3
2
1
0
KCOL Register(1)
VDD
KSIZE Register
7
6
5
4
3
2
1
0
Keypad Clock
Row Value
6
Debouncing
7
6
5
4
3
2
1
0
KROW Register
Hardware Scan Enable
If smaller keypad than 6 x 5 is to be
implemented, unused row inputs
should be connected to VDD. Unused
column outputs should be left
unconnected.
7
6
5
4
3
2
1
0
6
(1) KCOL is normally used as Read only
register. When hardware keyscan mode
is disabled, this register is to be used by
firmware to write the column data to
handle firmware scanning.
(2) 1kHz internal clock signal can be
selected either from the PLL (= from the
12MHz main clock), or from the 32kHz
system clock.
KSTAT Register
0
1
2
3
4
5
6
7
KSCAN Register
1kHz (2)
Dividers
73S1215F
Figure 12: Simplified Keypad Block Diagram
There are 5 drive lines (outputs) corresponding to columns and 6 sense lines (inputs) corresponding to
rows. Hysteresis and pull-ups are provided on all inputs (rows), which eliminate the need for external
resistors in the keypad. Key scanning happens by asserting one of the 5 column lines low and looking for
a low on a sense line indicating that a key is pressed (switch closed) at the intersection of the drive/sense
(col/row) line in the keypad. Key detection is performed by hardware with an incorporated debounce
timer. Debouncing time is adjustable through the KSCAN register. Internal hardware circuitry performs
column scanning at an adjustable scanning rate and column scanning order through registers KSCAN
and KORDERL / KORDERH. Key scanning is disabled at reset and must be enabled by firmware. When
a valid key is detected, an interrupt is generated and the valid value of the pressed key is automatically
written into KCOL and KROW registers. The keypad interface uses a 1kHz clock derived from either the
Rev. 1.4
65
TERIDIAN [ TERIDIAN SEMICONDUCTOR CORPORATION ]
