MAX6957 MAXIM [Maxim Integrated Products], MAX6957 Datasheet - Page 7

• Manufacturer Part Number: MAX6957
• Description: 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and 28-Port LED Display Driver and I/O Expander
• Manufacturer: MAXIM [Maxim Integrated Products]

The MAX6957 communicates through an SPI-compati-
ble 4-wire serial interface. The interface has three
inputs, Clock (SCLK), Chip Select
(DIN), and one output, Data Out (DOUT). CS must be
low to clock data into or out of the device, and DIN
must be stable when sampled on the rising edge of
SCLK. DOUT provides a copy of the bit that was input
15.5 clocks earlier, or upon a query it outputs internal
register data, and is stable on the rising edge of SCLK.
Note that the SPI protocol expects DOUT to be high
impedance when the MAX6957 is not being accessed;
DOUT on the MAX6957 is never high impedance.
SCLK and DIN may be used to transmit data to other
peripherals, so the MAX6957 ignores all activity on
Figure 1. MAX6957 Functional Diagram
LED DRIVERS
P4 TO P31
28-Port LED Display Driver and I/O Expander
OR GPIO
4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
SCLK
DIN
CS
_______________________________________________________________________________________
D0
D0
SEGMENT OR
GPIO DATA
LED DRIVERS AND GPIO
D1
D1
8
Serial Interface
D2
D2
CONFIGURATION
(CS), and Data In
D3
D3
DATA BYTE
INTENSITY
R/W
8
TEST
D4
D4
D5
D5
D6
D6
D7
D7
SCLK and DIN except between the fall and subsequent
rise of CS.
Controlling the MAX6957 requires sending a 16-bit
word. The first byte, D15 through D8, is the command
address (Table 3), and the second byte, D7 through
D0, is the data byte (Table 4).
Multiple MAX6957s may be daisy-chained by connect-
ing the DOUT of one device to the DIN of the next, and
driving SCLK and CS lines in parallel (Figure 4). Data at
DIN propagates through the internal shift registers and
appears at DOUT 15.5 clock cycles later, clocked out
on the falling edge of SCLK. When sending commands
PORT CHANGE
DETECTOR
D8
D8
Connecting Multiple MAX6957s to the 4-Wire Bus
Control and Operation Using the
D9
D9
D10
D10
COMMAND BYTE
D11
D11
D12
D12
REGISTER DECODE
DATA
INTENSITY REGISTERS
COMMAND
PORT REGISTERS
TEST REGISTER
8
MASK REGISTER
CONFIGURATION
D13
D13
8
REGISTERS
4-Wire Interface
CE
D14
D14
R/W
D15
D15
DOUT
7