Datasheet
MAX5803/MAX5804/MAX5805
Ultra-Small, Single-Channel, 8-/10-/12-Bit Buffered Output
Voltage DACs with Internal Reference and I
2
C Interface
18Maxim Integrated
I
2
C Broadcast Address
A broadcast address is provided for the purpose of
updating or configuring all MAX5803/MAX5804/MAX5805
devices on a given I
2
C bus. All MAX5803/MAX5804/
MAX5805 devices acknowledge and respond to the
broadcast device address 00110010. The broadcast
mode is intended for use in write mode only (as indicated
by R/W = 0 in the address given).
I
2
C Acknowledge
In write mode, the acknowledge bit (ACK) is a clocked
9th bit that the MAX5803/MAX5804/MAX5805 use to
handshake receipt of each byte of data as shown in
Figure 3. The MAX5803/MAX5804/MAX5805 pull down
SDA during the entire master-generated 9th clock pulse
if the previous byte is successfully received. Monitoring
ACK allows for detection of unsuccessful data transfers.
An unsuccessful data transfer occurs if a receiving
device is busy or if a system fault has occurred. In the
event of an unsuccessful data transfer, the bus master
will retry communication.
In read mode, the master pulls down SDA during the
9th clock cycle to acknowledge receipt of data from the
MAX5803/MAX5804/MAX5805. An acknowledge is sent
by the master after each read byte to allow data transfer
to continue. A not-acknowledge is sent when the master
reads the final byte of data from the MAX5803/MAX5804/
MAX5805, followed by a STOP condition.
I
2
C Command Byte and Data Bytes
A command byte follows the slave address. A command
byte is typically followed by two data bytes unless it
is the last byte in the transmission. If data bytes follow
the command byte, the command byte indicates the
address of the register that is to receive the following
two data bytes. The data bytes are stored in a temporary
register and then transferred to the appropriate register
during the ACK periods between bytes. This avoids any
glitching or digital feedthrough to the DAC while the
interface is active.
I
2
C Write Operations
A master device communicates with the MAX5803/
MAX5804/MAX5805 by transmitting the proper slave
address followed by command and data words. Each
transmit sequence is framed by a START or Repeated
START condition and a STOP condition as described
above. Each word is 8 bits long and is always followed
by an acknowledge clock (ACK) pulse as shown in
Figure 4 and Figure 5. The first byte contains the address
of the MAX5803/MAX5804/MAX5805 with R/W = 0 to
indicate a write. The second byte contains the register
(or command) to be written and the third and fourth bytes
contain the data to be written. By repeating the register
address plus data pairs (Byte #2 through Byte #4 in
Figure 4 and Figure 5), the user can perform multiple
register writes using a single I
2
C command sequence.
There is no limit as to how many registers the user can
write with a single command. The MAX5803/MAX5804/
MAX5805 support this capability for all user-accessible
write mode commands.
Combined Format I
2
C Readback Operations
Each readback sequence is framed by a START or
Repeated START condition and a STOP condition. Each
word is 8 bits long and is followed by an acknowledge
clock pulse as shown in Figure 6. The first byte contains
the address of the MAX5803/MAX5804/MAX5805 with
R/W = 0 to indicate a write. The second byte contains
the register that is to be read back. There is a Repeated
START condition, followed by the device address with
R/W = 1 to indicate a read and an acknowledge clock.
The master has control of the SCL line but the MAX5803/
MAX5804/MAX5805 take over the SDA line. The final two
bytes in the frame contain the register data readback
followed by a STOP condition. If additional bytes beyond
those required to readback the requested data are
provided, the MAX5803/MAX5804/MAX5805 will continue
to readback ones. Readback of the RETURN register
is supported for the RETURN command (B[23:20] =
0111). Readback of the CODE register is supported for
the CODE command (B[23:20] = 1000). Readback of
the DAC register is supported for all LOAD commands
(B[23:20] = 1001, 1010, or 1011).
Figure 3. I
2
C Acknowledge
1
SCL
START
CONDITION
SDA
29
CLOCK PULSE
FOR
ACKNOWLEDGMENT
ACKNOWLEDGE
NOT ACKNOWLEDGE