Datasheet

Control and Operation Using the
4-Wire Interface
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).
Connecting Multiple MAX6957s
to the 4-Wire Bus
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 to
multiple MAX6957s, all devices are accessed at the same
time. An access requires (16 × n) clock cycles, where n is
the number of MAX6957s connected together. To update
just one device in a daisy-chain, the user can send the
No-Op command (0x00) to the others.
Writing Device Registers
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
register.
3) Clock 16 bits of data into DIN—D15 first, D0 last—
observing the setup and hold times (bit D15 is low,
indicating a write command).
4) Take CS high (either while SCLK is still high after
clocking in the last data bit, or after taking SCLK low).
5) Take SCLK low (if not already low).
Figure 5 shows a write operation when 16 bits are
transmitted.
Figure 5. 16-Bit Write Transmission to the MAX6957
Figure 4. Daisy-Chain Arrangement for Controlling Multiple MAX6957s
.
D15
= 0
D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
D15 = 0
CS
SCLK
DIN
DOUT
MICROCONTROLLER
SERIAL DATA OUTPUT
SERIAL CLOCK OUTPUT
SERIAL DATA INPUT
DIN
SCLK
CS
DOUT
DIN
SCLK
CS
DOUT
DIN
SCLK
CS
DOUT
SERIAL CS OUTPUT
MAX6957MAX6957MAX6957
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