Rainbow Electronics W90P710CDG - Manual (Page 504)

W90P710CD/W90P710CDG
Publication Release Date: September 19, 2006
- 505 - Revision B2
Continued
BITS DESCRIPTION
[18] ENKP
Key pad scan enable
Setting this bit high enable the key scan function.
1 = enable key pad scan
0 = disable key pad scan
[17:16] KSIZE
Key array size
KSIZE Key array size
2’b00 4x8, 3x8, 2x8, 1x8
2’b01 8x8, 7x8, 6x8, 5x8
2’b1x 16x8, 15x8, 14x8, 13x8, 12x8, 11x8, 10x8, 9x8
[15:8] DBTC
Debounce terminal count
Debounce counter counts the number of consecutive scans that
decoded the same keys. When de-bounce counter counter is equal
to terminal count it will generate a key scan interrupt.
[7:0] PRESCALE
Row scan cycle pre-scale value
This value is used to prescale row scan cycle. The prescale counter
is clocked by 0.9375MHz clock.
Key array scan time = 1.067us x PRESCALE x16 ROWS
The following example is the scan time for PRESCALE = 0xFA
Tscan_time = 1.067us x 250 x16 = 4.268ms
If debounce terminal count = 0x05, key detection interrupt is fired in
approximately 21.34ms. The array scan time can range from
17.07us to 1.118 sec.