MAX6955 Maxim, MAX6955 Datasheet - Page 16

• Manufacturer Part Number: MAX6955
• Description: 2-Wire Interfaced / 2.7V to 5.5V LED Display Driver with I/O Expander and Key Scan
• Manufacturer: Maxim

The timing in Figure 12 loops over time, with 32 keys
experiencing a full key-scanning debounce over typi-
cally 25.6ms. Four keys are sampled every 1.6ms, or
every multiplex cycle. If at least one key that was not
previously pressed is found to have been pressed dur-
ing both sampling periods, then that key press is
debounced, and an interrupt is issued. The key-scan
circuit detects any combination of keys being pressed
during each debounce cycle (n-key rollover).
The port configuration register selects how the five port
pins are used. The port configuration register format is
described in Table 33.
2-Wire Interfaced, 2.7V to 5.5V LED Display
Driver with I/O Expander and Key Scan
Figure 7. Command Byte Received
Figure 8. Command and Single Data Byte Received
Figure 9. n Data Bytes Received
16
S
S
______________________________________________________________________________________
S
HOW CONTROL BYTE AND DATA BYTE MAP INTO
HOW CONTROL BYTE AND DATA BYTE MAP INTO
SLAVE ADDRESS
SLAVE ADDRESS
COMMAND BYTE IS STORED ON RECEIPT OF STOP CONDITION
ACKNOWLEDGE FROM MAX6955
ACKNOWLEDGE FROM MAX6955
Port Configuration Register
SLAVE ADDRESS
MAX6955's REGISTERS
MAX6955's REGISTERS
R/W
R/W
0
ACKNOWLEDGE FROM MAX6955
0
A
A
D15
D15
R/W
D14
D14
D13
D13
0
ACKNOWLEDGE FROM MAX6955
COMMAND BYTE
ACKNOWLEDGE FROM MAX6955
COMMAND BYTE
D12
D12
A
D11
D11
D15
D10
The Key_A Mask, Key_B Mask, Key_C Mask, and
Key_D Mask write-only registers (Table 34) 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.
D10
D9
D14
D9
D8
D8
D13
COMMAND BYTE
A
A
D12
D7
D7
ACKNOWLEDGE FROM MAX6955
D6
D6
D11
D5
D5
D10
AUTOINCREMENT MEMORY WORD ADDRESS
AUTOINCREMENT MEMORY WORD ADDRESS
ACKNOWLEDGE FROM MAX6955
ACKNOWLEDGE FROM MAX6955
D4
D4
1 BYTE
DATA BYTE
n BYTE
DATA BYTE
D3
D3
D 9
Key Mask Registers
D2
D2
D 8
D1
D1
A
D0
D0
A
A
P
P
P