EVAL-AD5551/52EB Analog Devices Inc, EVAL-AD5551/52EB Datasheet - Page 11

• Manufacturer Part Number: EVAL-AD5551/52EB
• Manufacturer: Analog Devices Inc

Specifications of EVAL-AD5551/52EB

• Lead Free Status / Rohs Status: Not Compliant

The 80C51/80L51 provides the LSB first, while the AD5551/
AD5552 expects the MSB of the 14-bit word first. Care should be
taken to ensure the transmit routine takes this into account.
Usually it can be done through software by shifting out and accu-
mulating the bits in the correct order before inputting to the DAC.
Also, 80C51 outputs 2 byte words/16 bits data, thus the first two
bits, after rearrangement, should be DON’T CARE as they will
be dropped from the DAC’s 14-bit word.
When data is to be transmitted to the DAC, P3.3 is taken low.
Data on RxD is valid on the falling edge of TxD, so the clock must
be inverted as the DAC clocks data into the input shift register on
the rising edge of the serial clock. The 80C51/80L51 transmits
its data in 8-bit bytes with only eight falling clock edges occur-
ring in the transmit cycle. As the DAC requires a 14-bit word,
P3.3 (or any one of the other programmable bits) is the CS input
signal to the DAC, so P3.3 should be brought low at the begin-
ning of the 16-bit write cycle 2 × 8 bit words and held low until
the 16-bit 2 × 8 cycle is completed. After that, P3.3 is brought
high again and the new data loads to the DAC. Again, the first
two bits, after rearranging, should be DON’T CARE. LDAC
on the AD5552 may also be controlled by the 80C51/80L51 serial
port output by using another bit programmable pin, P3.4.
APPLICATIONS
Optocoupler interface
The digital inputs of the AD5551/AD5552 are Schmitt-
triggered, so they can accept slow transitions on the digital input
lines. This makes these parts ideal for industrial applications
where it may be necessary that the DAC is isolated from the
controller via optocouplers. Figure 9 illustrates such an interface.
POWER
SCLK
DIN
CS
10k
10k
10k
V
V
V
DD
DD
DD
REGULATOR
SCLK
CS
DIN
5V
AD5551/AD5552
GND
V
DD
V
OUT
10 F
0.1 F
Decoding Multiple AD5551/AD5552s
The CS pin of the AD5551/AD5552 can be used to select one
of a number of DACs. All devices receive the same serial clock
and serial data, but only one device will receive the CS signal at
any one time. The DAC addressed will be determined by the
decoder. There will be some digital feedthrough from the digital
input lines. Using a burst clock will minimize the effects of digi-
tal feedthrough on the analog signal channels. Figure 10 shows a
typical circuit.
ADDRESS
ENABLE
CODED
SCLK
DIN
EN
DECODER
DGND
V
DD
AD5551/AD5552
CS
DIN
SCLK
CS
DIN
SCLK
CS
DIN
SCLK
CS
DIN
SCLK
AD5551/AD5552
AD5551/AD5552
AD5551/AD5552
AD5551/AD5552
V
V
V
V
OUT
OUT
OUT
OUT