Rainbow Electronics MAX6959 - Manual (Page 15)

pullup resistor from IRQ/SEG9 to a voltage no greater
than 5.5V when configuring IRQ/SEG9 as an interrupt
or logic output.
INPUT1 and INPUT2 can be individually configured as
either general-purpose logic inputs or as keyscan
inputs. In either mode, the input structure is the same—
CMOS logic inputs with internal pullup resistors. The
pullups are always enabled, even in shutdown. Ensure
these inputs are either close to V+ or open circuit for
minimum shutdown supply current. If both INPUT1 and
INPUT2 are assigned to keyscan, then eight keys can
be debounced. If only INPUT1 or INPUT2 is assigned
to keyscan, then only four keys can be debounced.
MAX6958/MAX6959
2-Wire Interfaced, 3V to 5.5V, 4-Digit,
9-Segment LED Display Drivers with Keyscan
______________________________________________________________________________________ 15
DIG1/SEG1
DIG2/SEG2
DIG3/SEG3
DIG0/SEG0
THE FIRST HALF OF A 41ms KEYSCAN CYCLE THE SECOND HALF OF A 41ms KEYSCAN CYCLE
A B
START OF NEXT KEYSCAN CYCLE
INTERRUPT ASSERTED IF REQUIRED
KEY DEBOUNCED REGISTER UPDATED
1.28ms MULTIPLEX
CYCLE 1
INPUT2
INPUT1 Key0
FIRST TEST OF KEYS SECOND TEST OF KEYS
t DEBOUNCE
Key1 Key2 Key3
Key4 Key5 Key6 Key7
Key0 Key1 Key2 Key3
Key4 Key5 Key6 Key7
C D E
A
1.28ms MULTIPLEX
CYCLE 2
1.28ms MULTIPLEX
CYCLE 3
1.28ms MULTIPLEX
CYCLE 4
1.28ms MULTIPLEX
CYCLE 15
1.28ms MULTIPLEX
CYCLE 16
1.28ms MULTIPLEX
CYCLE 1
1.28ms MULTIPLEX
CYCLE 2
1.28ms MULTIPLEX
CYCLE 15
1.28ms MULTIPLEX
CYCLE 16
5 µs TO 315µs DIGIT PERIOD
Figure 14. Keyscan Timing Diagram
REGISTER DATA
MODE
ADDRESS
CODE
(HEX)
D7 D6 D5 D4 D3 D2 D1 D0
This is the bit assignment:
Read GPIO register 0x06
Read back
IRQ/SEG9
configuration Read back
INPUT 2
configuration Read back
INPUT 1
configuration
INPUT2
logic level INPUT1
logic level IRQ status
( 1 = i nter rup t)
Write GPIO register 0x06
Configure
IRQ/SEG9
output
Configure
INPUT 2:
0 = logic input
1 = keyscan Configure
INPUT 1:
0 = logic input
1 = keyscan
X X X
Here are the IRQ/SEG9 allocation options, determined by the settings of D7, D6, D5:
IRQ/SEG9 is logic 0 output 0x06 0 0 0 X X X X X
IRQ/SEG9 is logic 1 output 0x06 0 0 1 X X X X X
IRQ/SEG9 is active-low
IRQ
0x06 0 1 0 X X X X X
IRQ/SEG9 is active-high
IRQ
0x06 0 1 1 X X X X X
IRQ/SEG9 is segment
driver
0x06 1 X X X X X X X
Table 16. Port Configuration Register Format