MAX6955 Maxim, MAX6955 Datasheet - Page 10

• 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

2-Wire Interfaced, 2.7V to 5.5V LED Display
Driver with I/O Expander and Key Scan
Table 5. MAX6955 Address Map
The MAX6955 is read using the MAX6955’s internally
stored command byte as address pointer, the same
way the stored command byte is used as address
pointer for a write. The pointer generally autoincre-
ments after each data byte is read using the same rules
as for a write (Table 6). Thus, a read is initiated by first
configuring the MAX6955’s command byte by perform-
ing a write (Figure 7). The master can now read n con-
secutive bytes from the MAX6955, with the first data
byte being read from the register addressed by the ini-
tialized command byte (Figure 9). When performing
read-after-write verification, reset the command byte’s
address because the stored byte address generally is
autoincremented after the write (Table 6).
10
Table 6. Command Address Autoincrement Rules
PIN CONNECTION
GND
GND
GND
GND
AD1
SDA
SDA
SDA
SDA
SCL
SCL
SCL
SCL
V+
V+
V+
V+
______________________________________________________________________________________
x0000000 to x0001100
x0001111 to x1111110
ADDRESS RANGE
COMMAND BYTE
x0001101
x1111111
GND
GND
GND
GND
AD0
SDA
SDA
SDA
SDA
SCL
SCL
SCL
SCL
V+
V+
V+
V+
Message Format for Reading
A6
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
A5
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
DEVICE ADDRESS
A4
Command byte address autoincrements after byte read or written.
Factory reserved; do not write this register.
Command byte address autoincrements after byte read or written.
Command byte address remains at x1111111 after byte read or written.
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
A3
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
A2
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
A1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
A0
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
AUTOINCREMENT BEHAVIOR
If the MAX6955 is operated on a 2-wire interface with
multiple masters, a master reading the MAX6955
should use a repeated start between the write, which
sets the MAX6955’s address pointer, and the read(s)
that takes the data from the location(s). This is because
it is possible for master 2 to take over the bus after
master 1 has set up the MAX6955’s address pointer but
before master 1 has read the data. If master 2 subse-
quently changes the MAX6955’s address pointer, then
master 1’s delayed read may be from an unexpected
location.
Address autoincrementing allows the MAX6955 to be
configured with the shortest number of transmissions
by minimizing the number of times the command byte
needs to be sent. The command address or the font
pointer address stored in the MAX6955 generally incre-
ments after each data byte is written or read (Table 6).
The MAX6955 uses 32 digit registers to store the char-
acters that the user wishes to display. These digit regis-
ters are implemented with two planes, P0 and P1. Each
digit is represented by 2 bytes of memory, 1 byte in
plane P0 and the other in plane P1. The digit registers
are mapped so that a digit’s data can be updated in
plane P0, plane P1, or both planes at the same time
(Table 7).
If the blink function is disabled through the Blink Enable
Bit E (Table 20) in the configuration register, then the
digit register data in plane P0 is used to multiplex the
display. The digit register data in P1 is not used. If the
blink function is enabled, then the digit register data in
both plane P0 and plane P1 are alternately used to mul-
tiplex the display. Blinking is achieved by multiplexing
the LED display using data plane P0 and plane P1 on
alternate phases of the blink clock (Table 21).
The data in the digit registers does not control the digit
segments directly for 14- and 16-segment displays.
Instead, the register data is used to address a charac-
ter generator that stores the data for the 14- and 16-
Command Address Autoincrementing
Operation with Multiple Masters
Digit Type Registers