Datasheet

Shutdown mode is temporarily overridden by the dis-
play test function.
Serial Interface
Serial Addressing
The MAX6956 operates as a slave that sends and
receives data through an I
2
C-compatible 2-wire inter-
face. The interface uses a serial data line (SDA) and a
serial clock line (SCL) to achieve bidirectional commu-
nication between master(s) and slave(s). A master (typ-
ically a microcontroller) initiates all data transfers to and
from the MAX6956, and generates the SCL clock that
synchronizes the data transfer (Figure 2).
The MAX6956 SDA line operates as both an input and
an open-drain output. A pullup resistor, typically 4.7kΩ,
is required on SDA. The MAX6956 SCL line operates
only as an input. A pullup resistor, typically 4.7kΩ, is
required on SCL if there are multiple masters on the 2-
wire interface, or if the master in a single-master system
has an open-drain SCL output.
Each transmission consists of a START condition
(Figure 3) sent by a master, followed by the MAX6956
7-bit slave address plus R/W bit (Figure 6), a register
address byte, one or more data bytes, and finally a
STOP condition (Figure 3).
Start and Stop Conditions
Both SCL and SDA remain high when the interface is
not busy. A master signals the beginning of a transmis-
sion with a START (S) condition by transitioning SDA
from high to low while SCL is high. When the master
MAX6956
2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or
28-Port LED Display Driver and I/O Expander
_______________________________________________________________________________________________________ 7
SLAVE ADDRESS BYTE
D0 D1 D2 D3 D4 D5 D6 D7 D8 D9 D10 D11 D12 D13 D14 D15
R/W
8
8
CEDATA
8
SDA
SCL
TEST REGISTER
INTENSITY REGISTERS
PORT REGISTERS
LED DRIVERS AND GPIO
INTENSITY
CONFIGURATION
TEST
P4 TO P31
LED DRIVERS
OR GPIO
ADDRESS
MATCHER
AD0
AD1
COMMAND BYTEDATA BYTE
R/W7-BIT DEVICE ADDRESS
7
7
TO COMMAND REGISTERS
TO/FROM DATA REGISTERS
SEGMENT OR
GPIO DATA
R/W
CONFIGURATION
REGISTERS
PORT CHANGE
DETECTOR
MASK REGISTER
COMMAND
REGISTER DECODE
8
DATA BYTE COMMAND BYTE
MAX6956
Figure 1. MAX6956 Functional Diagram