MAX6954 Maxim, MAX6954 Datasheet - Page 15

• Manufacturer Part Number: MAX6954
• Description: 4-Wire Interfaced / 2.7V to 5.5V LED Display Driver with I/O Expander and Key Scan
• Manufacturer: Maxim

Table 6. Register Address Map (continued)
Note: Unused register bits read as zero.
The port configuration register selects how the five port
pins are used. The port configuration register format is
described in Table 32.
The Key_A Mask, Key_B Mask, Key_C Mask, and
Key_D Mask write-only registers (Table 33) configure
the key-scanning circuit to cause an interrupt only when
selected (masked) keys have been debounced. Each
bit in the register corresponds to one key switch. The bit
is clear to disable interrupt for the switch, and set to
enable interrupt. Keys are always scanned (if enabled
through the port configuration register), regardless of
the setting of these interrupt bits, and the key status is
stored in the appropriate Key_x pressed register.
The Key_A debounced, Key_B debounced, Key_C
debounced, and Key_D debounced read-only registers
(Table 34) show which keys have been detected as
debounced by the key-scanning circuit.
Each bit in the register corresponds to one key switch.
The bit is set if the switch has been correctly
debounced since the register was read last. Reading a
debounced register clears that register (after the data
has been read) so that future keys pressed can be
identified. If the debounced registers are not read, the
key-scan data accumulates. However, as there is no
FIFO in the MAX6954, the user is not able to determine
Write Digit 2a Planes P0 and P1 with Same
Data (7 Segment Only), Reads as 0x00
Write Digit 3a Planes P0 and P1 with Same
Data (7 Segment Only), Reads as 0x00
Write Digit 4a Planes P0 and P1 with Same
Data (7 Segment Only), Reads as 0x00
Write Digit 5a Planes P0 and P1 with Same
Data (7 Segment Only), Reads as 0x00
Write Digit 6a Planes P0 and P1 with Same
Data (7 Segment Only), Reads as 0x00
Write Digit 7a Planes P0 and P1 with Same
Data (7 Segment Only), Reads as 0x00
4-Wire Interfaced, 2.7V to 5.5V LED Display
REGISTER
______________________________________________________________________________________
Port Configuration Register
Driver with I/O Expander and Key Scan
Key Debounced Registers
Key Mask Registers
D15
R/W
R/W
R/W
R/W
R/W
R/W
D14
1
1
1
1
1
1
ADDRESS (COMMAND BYTE)
D13
1
1
1
1
1
1
key order, or whether a key has been pressed more
than once, unless the debounced key status registers
are read after each interrupt, and before the next key-
scan cycle.
Reading any of the four debounced registers clears the
IRQ output. If a key is pressed and held down, the key
is reported as debounced (and IRQ issued) only once.
The key must be detected as released by the key-scan-
ning circuit, before it debounces again. If the
debounced registers are being read in response to the
IRQ being asserted, then the user should generally read
all four registers to ensure that all the keys that were
detected by the key-scanning circuit are discovered.
The Key_A pressed, Key_B pressed, Key_C pressed,
and Key_D pressed read-only registers (Table 35)
show which keys have been detected as pressed by
the key-scanning circuit during the last test.
Each bit in the register corresponds to one key switch.
The bit is set if the switch has been detected as
pressed by the key-scanning circuit during the last test.
D12
0
0
0
0
0
0
D11
1
1
1
1
1
1
D10
0
0
1
1
1
1
D9
1
1
0
0
1
1
Key Pressed Registers
D8
0
1
0
1
0
1
HEX CODE
0x6A
0x6B
0x6C
0x6D
0x6E
0x6F
15