AD8804 Analog Devices, AD8804 Datasheet - Page 10

• Manufacturer Part Number: AD8804
• Description: 12 Channel, 8-Bit TrimDACs with Power Shutdown & Separate VREFL Input
• Manufacturer: Analog Devices

Specifications of AD8804

• Resolution (bits): 8bit
• Dac Update Rate: 1.7MSPS
• Dac Settling Time: 600ns
• Max Pos Supply (v): +5.5V
• Single-supply: Yes
• Dac Type: Voltage Out
• Dac Input Format: Ser,SPI

AD8802/AD8804
;
; This subroutine loads an AD8802/AD8804 DAC from an 8051 microcomputer,
; using the 8051’s serial port in MODE 0 (Shift Register Mode).
; The DAC value is stored at location DAC_VAL
; The DAC address is stored at location DAC_ADDR
;
; Variable declarations
;
PORT1
DAC_VALUE
DAC_ADDR
SHIFT1
SHIFT2
SHIFT_COUNT
;
DO_8802:
ADDR_WAIT:
VALU_WAIT:
;
BYTESWAP:
SWAP_LOOP:
Figure 25. An AD8802/AD8804-8051 C Interface Using
Parallel Port 1
PORT 1
8051 µC
1.7
1.6
1.5
1.4
DATA
DATA
DATA
DATA
DATA
DATA
ORG
CLR
CLR
CLR
CLR
ORL
CLR
MOV
ACALL
MOV
JNB
CLR
MOV
ACALL
MOV
JNB
CLR
SETB
RET
MOV
MOV
RLC
MOV
MOV
RRC
MOV
DJNZ
RET
END
Listing 1. Software for the 8051 to AD8802/AD8804 Serial Port Interface
P1.7
P1.6
P1.5
P1.4
SDI
CLK
CS
SHDN
V
GND
+5V
AD8804
DD
V
V
REFH
REFL
O12
90H
40H
41H
042H
043H
44H
100H
SCON.7
SCON.6
SCON.1
PORT1.1,#00001110B
PORT1.1
SHIFT1,DAC_ADDR
BYTESWAP
SBUF,SHIFT2
SCON.1,ADDR_WAIT
SCON.1
SHIFT1,DAC_VALUE
BYTESWAP
SBUF,SHIFT2
SCON.1,VALU_WAIT
SCON.1
PORT1.1
SHIFT_COUNT,#8
A,SHIFT1
A
SHIFT1,A
A,SHIFT2
A
SHIFT2,A
SHIFT_COUNT,SWAP_LOOP
SCON.5
O1
–10–
to start the serial interface process. The DAC address is loaded
into the accumulator and four Rotate Right shifts are per-
formed. This places the DAC address in the 4 MSBs of the ac-
cumulator. The address is then sent to the AD8802/AD8804 via
the SEND_SERIAL subroutine. Next, the DAC value is loaded
into the accumulator and sent to the AD8802/AD8804. Finally,
the Chip Select input is set high to complete the data transfer
Unlike the serial port interface of Figure 24, the parallel port in-
terface only transmits 12 bits to the AD8802/AD8804. Also, the
BYTESWAP subroutine is not required for the parallel inter-
face, because data can be shifted out MSB first. However, the
results of the two interface methods are exactly identical. In
most cases, the decision on which method to use will be deter-
mined by whether or not the serial data port is available for
communication with the AD8802/AD8804.
;SFR register for port 1
;DAC Value
;DAC Address
;high byte of 16-bit answer
;low byte of answer
;
;arbitrary start
;set serial
;data mode 0
;clr transmit flag
;/RS, /SHDN, /CS high
;set the /CS low
;put DAC value in shift register
;
;send the address byte
;wait until 8 bits are sent
;clear the serial transmit flag
;send the DAC value
;
;
;wait again
;clear serial flag
;/CS high, latch data
; into AD8801
;Shift 8 bits
;Get source byte
;Rotate MSB to carry
;Save new source byte
;Get destination byte
;Move carry to MSB
;Save
;Done?
REV. 0