MAX6957 MAXIM [Maxim Integrated Products], MAX6957 Datasheet - Page 9

• 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]

to multiple MAX6957s, all devices are accessed at the
same time. An access requires (16
where n is the number of MAX6957s connected togeth-
er. To update just one device in a daisy-chain, the user
can send the No-Op command (0x00) to the others.
The MAX6957 contains a 16-bit shift register into which
DIN data are clocked on the rising edge of SCLK, when
CS is low. When CS is high, transitions on SCLK have
no effect. When CS goes high, the 16 bits in the Shift
register are parallel loaded into a 16-bit latch. The 16
bits in the latch are then decoded and executed.
The MAX6957 is written to using the following
sequence:
1) Take SCLK low.
2) Take CS low. This enables the internal 16-bit shift
3) Clock 16 bits of data into DIN—D15 first, D0 last—
Figure 4. Daisy-Chain Arrangement for Controlling Multiple MAX6957s
Figure 5. 16-Bit Write Transmission to the MAX6957
DOUT
SCLK
DIN
register.
observing the setup and hold times (bit D15 is low,
indicating a write command).
CS
28-Port LED Display Driver and I/O Expander
MICROCONTROLLER
4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
SERIAL CLOCK OUTPUT
SERIAL DATA OUTPUT
SERIAL DATA INPUT
SERIAL CS OUTPUT
D15
= 0
_______________________________________________________________________________________
D14
Writing Device Registers
D13
D12
CS
SCLK
DIN
✕
D11
n) clock cycles,
MAX6957
D10
DOUT
D9
D8
4) Take CS high (while SCLK is still high after clocking
5) Take SCLK low.
Figure 5 shows a write operation when 16 bits are
transmitted.
It is acceptable to clock more than 16 bits into the
MAX6957 between taking CS low and taking CS high
again. In this case, only the last 16 bits clocked into the
MAX6957 are retained.
Any register data within the MAX6957 may be read by
sending a logic high to bit D15. The sequence is:
1) Take SCLK low.
2) Take CS low (this enables the internal 16-bit shift
3) Clock 16 bits of data into DIN—D15 first to D0 last.
D7
CS
SCLK
DIN
in the last data bit).
register).
D15 is high, indicating a read command and bits
D14 through D8 containing the address of the reg-
ister to be read. Bits D7–D0 contain dummy data,
which is discarded.
.
D6
MAX6957
D5
DOUT
D4
Reading Device Registers
D3
CS
SCLK
DIN
D2
MAX6957
D1
DOUT
D0
D15 = 0
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