Rainbow Electronics MAX518 User Manual
Page 12
MAX517/MAX518/MAX519
2-Wire Serial 8-Bit DACs with
Rail-to-Rail Outputs
12
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Additional START Conditions
It is possible to interrupt a transmission to a device with
a new START (repeated start) condition (perhaps
addressing another device), which leaves the input
latches with data that has not been transferred to the
output latches (Figure 13). Only the currently addressed
device will recognize a STOP condition and transfer
data to its output latches. If the device is left with data in
its input latches, the data can be transferred to the out-
put latches the next time the device is addressed, as
long as it receives at least one command byte and a
STOP condition.
Early STOP Conditions
The addressed device recognizes a STOP condition at
any point in a transmission. If the STOP occurs during a
command byte, all previous uninterrupted command
and output byte pairs are accepted, the interrupted
command byte is ignored, and the transmission ends
(Figure 14a). If the STOP occurs during an output byte,
all previous uninterrupted command and output byte
pairs are accepted, the final command byte’s PD and
RST bits are accepted, the interrupted output byte is
ignored, and the transmission ends (Figure 14b).
Analog Section
DAC Operation
The MAX518 and MAX519 contain two matched volt-
age-output DACs. The MAX517 contains a single DAC.
The DACs are inverted R-2R ladder networks that con-
vert 8-bit digital words into equivalent analog output
voltages in proportion to the applied reference volt-
ages. The MAX518 has both DAC’s reference inputs
connected to V
DD
. Figure 15 shows a simplified dia-
gram of one DAC.
MAX517/MAX519 Reference Inputs
The MAX517 and MAX519 can be used for multiplying
applications. The reference accepts a 0V to V
DD
volt-
( )
( )
( )
SDA
0
START
CONDITION
ADDRESS BYTE
(DEVICE 0)
ACK
1
0
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
1
1
0
1
0
0
1
REPEATED START
CONDITION
STOP
CONDITION
COMMAND BYTE
ADDRESSING DAC0
COMMAND BYTE
(ADDRESSING DAC0)
ACK
OUTPUT BYTE
(FULL SCALE)
ACK
ADDRESS BYTE
(DEVICE 1)
ACK
DEVICE 0's
DAC0 INPUT LATCH
SET TO FULL SCALE.
DEVICE 1's DAC0
INPUT LATCH SET
TO FULL SCALE.
SDA
ACK
ACK
OUTPUT BYTE
(FULL SCALE)
ONLY DEVICE 1's DAC0 OUTPUT LATCH SET TO FULL
SCALE. DEVICE 0's OUTPUT LATCH UNCHANGED.
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
Figure 13. Repeated START Conditions
MAX518
SDA SCL
µC
SDA
SCL
E
2
PROM
XICOR
X24C04
SDA
SCL
AD1
AD0
DUAL
DAC
SDA
SCL
AD1
AD0
SINGLE
DAC
+5V
MAX517
OUT0
OUT1
OUT0
Figure 12. MAX517/MAX518/MAX519 Used in a Typical I
2
C
Application Circuit