Rainbow Electronics MAX5479 - Manual (Page 11)

MAX5477/MAX5478/MAX5479
Dual, 256-Tap, Nonvolatile, I
2
C-Interface,
Digital Potentiometers
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slave address is the NOP/W bit. Set the NOP/W bit low for
a write command and high for a no-operation command.
The MAX5477/MAX5478/MAX5479 provide three
address inputs (A0, A1, and A2), allowing up to eight
devices to share a common bus (Table 1). The first 4
bits (MSBs) of the MAX5477/MAX5478/MAX5479 slave
addresses are always 0101. A2, A1, and A0 set the next
3 bits in the slave address. Connect each address input
to V
DD
or GND to set these 3 bits. Each device must
have a unique address to share a common bus.
Message Format for Writing
Write to the MAX5477/MAX5478/MAX5479 by transmit-
ting the device’s slave address with NOP/W (8th bit) set
to zero, followed by at least 1 byte of information
(Figure 7). The 1st byte of information is the command
byte. The bytes received after the command byte are
the data bytes. The 1st data byte goes into the internal
register of the MAX5477/MAX5478/MAX5479 as select-
ed by the command byte (Figure 8).
Command Byte
Use the command byte to select the source and desti-
nation of the wiper data (nonvolatile or volatile memory
registers) and swap data between nonvolatile and
volatile memory registers (see Table 2).
Command Descriptions
VREG: The data byte writes to the volatile memory reg-
ister and the wiper position updates with the data in the
volatile memory register.
NVREG: The data byte writes to the nonvolatile memory
register. The wiper position is unchanged.
NVREGxVREG: Data transfers from the nonvolatile
memory register to the volatile memory register (wiper
position updates).
VREGxNVREG: Data transfers from the volatile memory
register into the nonvolatile memory register.
Nonvolatile Memory
The internal EEPROM consists of a 16-bit nonvolatile
register that retains the value written to it prior to power
down. The nonvolatile register is programmed with the
midscale value at the factory. The nonvolatile memory
is guaranteed for 50 years for wiper position retention
and up to 200,000 wiper write cycles. A write-protect
feature prevents accidental overwriting of the EEPROM.
Connect WP to V
DD or leave open to enable the write-
protect feature. The wiper position only updates with
the value in the EEPROM when WP = V
DD
. Connect WP
to GND to allow EEPROM write cycles and to update
the wiper position from nonvolatile memory or directly
from the I
2 C serial interface.
Power-Up
Upon power-up, the MAX5477/MAX5478/MAX5479
load the data stored in the nonvolatile memory register
into the volatile memory register, updating the wiper
position with the data stored in the nonvolatile memory
register. This initialization period takes 10µs.
A 0 SLAVE ADDRESS COMMAND BYTE DATA BYTE
ACKNOWLEDGE FROM
MAX5477/MAX5478/MAX5479
NOP/W 1 BYTE
ACKNOWLEDGE FROM
MAX5477/MAX5478/MAX5479
ACKNOWLEDGE FROM
MAX5477/MAX5478/MAX5479
D15 D14 D13 D12 D11 D10 D9 D8 D1 D0 D3 D2 D5 D4 D7 D6
HOW CONTROL BYTE AND DATA BYTE MAP INTO
MAX5477/MAX5478/MAX5479 REGISTERS
S A A P
S A 0 SLAVE ADDRESS COMMAND BYTE
ACKNOWLEDGE FROM
MAX5477/MAX5478/MAX5479
NOP/W
ACKNOWLEDGE FROM
MAX5477/MAX5478/MAX5479
D15 D14 D13 D12 D11 D10 D9 D8 COMMAND BYTE IS STORED ON RECEIPT OF STOP CONDITION
A P
Figure 7. Command Byte Received
Figure 8. Command and Single Data Byte Received