Rainbow Electronics MAX5484 - Manual (Page 16)

MAX5481–MAX5484
10-Bit, Nonvolatile, Linear-Taper Digital
Potentiometers
16 ______________________________________________________________________________________
Copy Wiper Register to NV Register
The copy wiper register to NV register command (C1,
C0 = 10) stores the current position of the wiper to the
NV register for use at power-up. Figure 6 shows how to
copy data from wiper register to NV register. The oper-
ation takes up to 12ms (max) after CS goes high to
complete and no other operation should be performed
until completion.
Copy NV Register to Wiper Register
The copy NV register to wiper register (C1, C0 = 11)
restores the wiper position to the current value stored in
the NV register. Figure 7 shows how to copy data from
the NV register to the wiper register.
Digital Up/Down Interface
Figure 8 illustrates an up/down serial-interface timing
diagram. In digital up/down interface mode (SPI/UD =
0), the logic inputs CS, DIN(U/D), and SCLK(INC) con-
trol the wiper position and store it in nonvolatile memory
(see Table 3). The chip-select (CS) input enables the
serial interface when low and disables the interface
when high. The position of the wiper is stored in the
nonvolatile register when CS transitions from low to
high while SCLK(INC) is high.
When the serial interface is active (CS low), a high-to-
low (falling edge) transition on SCLK(INC) increments
or decrements the internal 10-bit counter depending on
the state of DIN(U/D). If DIN(U/D) is high, the wiper
increments. If DIN(U/D) is low, the wiper decrements.
The device stores the value of the wiper position in the
nonvolatile memory when CS transitions from low to high
while SCLK(INC) is high. The host system can disable
the serial interface and deselect the device without stor-
ing the latest wiper position in the nonvolatile memory by
keeping SCLK(INC) low while taking CS high.
Upon power-up, the MAX5481–MAX5484 load the
value of nonvolatile memory into the wiper register, and
set the wiper position to the value last stored.
ACTION
0 0 1 0 0 0 0 0
1 2 3 4 5 6 7 8
CS
C1 C0
WRITE NV
REGISTER
(DEVICE IS
BUSY)
t BUSY
SCLK( INC)
DIN(U/ D)
Figure 6. Copy Wiper Register to NV Register Operation
CS DIN(U/D) SCLK(INC) W
L L ↓ Decrement
L H ↓ Increment
L X ↑ No Change
H X X No Change
↓ X X No Change
↑ X L Position Not Stored
↑ X H Position Stored
Table 3. Truth Table
↑ = High-to-low transition.
↓ = Low-to-high transition.
X = Don’t care.
ACTION
0 0 1 1 0 0 0 0
1 2 3 4 5 6 7 8
CS
C1 C0
WIPER
REGISTER
UPDATED
SCLK( INC)
DIN(U/ D)
Figure 7. Copy NV Register to Wiper Register Operation