Datasheet

Detailed Description
MAX7219/MAX7221 Di󰀨erences
The MAX7219 and MAX7221 are identical except for two
parameters: the MAX7221 segment drivers are slew-rate
limited to reduce electromagnetic interference (EMI), and
its serial interface is fully SPI compatible.
Serial-Addressing Modes
For the MAX7219, serial data at DIN, sent in 16-bit packets,
is shifted into the internal 16-bit shift register with each
rising edge of CLK regardless of the state of LOAD. For
the MAX7221, CS must be low to clock data in or out.
The data is then latched into either the digit or control registers
on the rising edge of LOAD/CS. LOAD/CS must go high
concurrently with or after the 16th rising clock edge, but
before the next rising clock edge or data will be lost.
Data at DIN is propagated through the shift register and
appears at DOUT 16.5 clock cycles later. Data is clocked
out on the falling edge of CLK. Data bits are labeled
D0–D15 (Table 1). D8–D11 contain the register address.
D0–D7 contain the data, and D12–D15 are “don’t care”
bits. The first received is D15, the most significant bit
(MSB).
Digit and Control Registers
Table 2 lists the 14 addressable digit and control registers.
The digit registers are realized with an on-chip, 8x8
dual-port SRAM. They are addressed directly so that
individual digits can be updated and retain data as long
as V+ typically exceeds 2V. The control registers consist
of decode mode, display intensity, scan limit (number of
scanned digits), shutdown, and display test (all LEDs on).
Shutdown Mode
When the MAX7219 is in shutdown mode, the scan oscillator is
halted, all segment current sources are pulled to ground,
and all digit drivers are pulled to V+, thereby blanking the
display. The MAX7221 is identical, except the drivers are
high-impedance. Data in the digit and control registers
remains unaltered. Shutdown can be used to save power
or as an alarm to flash the display by successively entering
and leaving shutdown mode. For minimum supply current
in shutdown mode, logic inputs should be at ground or V+
(CMOS-logic levels).
Typically, it takes less than 250μs for the MAX7219/
MAX7221 to leave shutdown mode. The display driver can
be programmed while in shutdown mode, and shutdown
mode can be overridden by the display-test function.
Figure 1. Timing Diagram
Table 1. Serial-Data Format (16 Bits)
D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
X X X X ADDRESS MSB DATA LSB
CLK
DIN D15
DOUT
D14 D1 D0
t
CSS
t
CL
t
CH
t
CP
t
DO
t
LDCK
t
CSW
t
CSH
t
DS
t
DH
CS
OR LOAD
MAX7219/MAX7221 Serially Interfaced, 8-Digit LED Display Drivers
www.maximintegrated.com
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