Datasheet

Shutdown
When the MAX6957 is in shutdown mode, all ports are
forced to inputs, and the pullup current sources are turned
off. Data in the port and control registers remain unaltered
so port configuration and output levels are restored when
the MAX6957 is taken out of shutdown. The display driv-
er can still be programmed while in shutdown mode. For
minimum supply current in shutdown mode, logic inputs
should be at GND or V+ potential. Shutdown mode is
exited by setting the S bit in the configuration register
(Table 6). Shutdown mode is temporarily overridden by
the display test function.
Serial Interface
The MAX6957 communicates through an SPI-compati-
ble 4-wire serial interface. The interface has three
inputs, Clock (SCLK), Chip Select (CS), and Data In
(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 imped-
ance. Go to www.maximintegrated.com/an1879 for
ways to convert DOUT to tri-state, if required.
SCLK and DIN may be used to transmit data to other
peripherals, so the MAX6957 ignores all activity on
SCLK and DIN except between the fall and subsequent
rise of CS.
Figure 1. MAX6957 Functional Diagram
D0 D1 D2 D3 D4 D5 D6 D7 D8 D9 D10 D11 D12 D13 D14 D15
D0 D1 D2 D3 D4 D5 D6 D7 D8 D9 D10 D11 D12 D13 D14 D15
R/W
8
CEDATA
8
TEST REGISTER
INTENSITY REGISTERS
PORT REGISTERS
LED DRIVERS AND GPIO
INTENSITY
CONFIGURATION
TEST
P4 TO P31
LED DRIVERS
OR GPIO
SEGMENT OR
GPIO DATA
R/W
CONFIGURATION
REGISTERS
PORT CHANGE
DETECTOR
MASK REGISTER
COMMAND
REGISTER DECODE
88
DATA BYTE COMMAND BYTE
CS
DIN
SCLK
DOUT
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Maxim Integrated │ 7
MAX6957 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander