JAJSFN6G September 2009 – June 2018 TCA8418
PRODUCTION DATA.
The first steps towards designing a keypad array is to determine the desired layout, and to map each key to the appropriate value which will show up in the FIFO. For this example, the number pad below is the physical location of the keys that are desired. The layout is a 4 x 3 array, using rows 0-3 and columns 0-2. For this example, we will not assume any of the other pins will be used.
The following behavior is desired for this example design
Since the TCA8418 reports keys pressed according to the values in the key value table, it is important to know the TCA8418 values for the key locations.
According to the key event table, the key presses are assigned in Table 12.
Keypad Button | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | * | 0 | # |
Key Event Table Value (Decimal) | 1 | 2 | 3 | 11 | 12 | 13 | 21 | 22 | 23 | 31 | 32 | 33 |
The schematic for this keypad layout is shown in figure (schematic below) with the key event table values. Note that no external pullup resistors are needed, because the TCA8418 has integrated pullup resistors.