AD7712 Analog Devices, AD7712 Datasheet - Page 25

• Manufacturer Part Number: AD7712
• Description: CMOS, 24-Bit Sigma-Delta, Signal Conditioning ADC with 2 Analog Input Channels
• Manufacturer: Analog Devices

Specifications of AD7712

• Resolution (bits): 24bit
• # Chan: 2
• Sample Rate: 19.5kSPS
• Interface: Ser
• Analog Input Type: Diff-Bip,Diff-Uni,SE-Bip
• Ain Range: Bip (Vref) x 4,Bip (Vref)/(PGA Gain),Bip 10V,Bip 20V,Uni (Vref) x 4,Uni (Vref)/(PGA Gain),Uni 10V,Uni 20V
• Adc Architecture: Sigma-Delta
• Pkg Type: DIP,SOIC

AD7712 to 8051 Interface
Figure 18 shows an interface between the AD7712 and the
8XC51 microcontroller. The AD7712 is configured for its
external clocking mode, while the 8XC51 is configured in its
Mode 0 serial interface mode. The DRDY line from the AD7712
is connected to the Port P1.2 input of the 8XC51, so the DRDY
line is polled by the 8XC51. The DRDY line can be connected
to the INT1 input of the 8XC51 if an interrupt driven system is
preferred.
REV. F
8XC51
Figure 17. Flowchart for Single Write Operation
to the AD7712
Figure 18. AD7712 to 8XC51 Interface
P1.0
P1.2
P1.3
P3.0
P1.1
P3.1
ACCUMULATOR TO
WRITE DATA FROM
LOAD DATA FROM
CONFIGURE AND
INITIALIZE C/ P
BRING RFS, TFS
ACCUMULATOR
SERIAL BUFFER
SERIAL PORT
AND A0 HIGH
ADDRESS TO
AND A0 LOW
AND A0 HIGH
ORDER OF
BRING TFS
BRING TFS
REVERSE
START
BITS
END
DV
DD
3
SYNC
RFS
DRDY
A0
SDATA
SCLK
MODE
TFS
AD7712
–25–
Table VII shows some typical 8XC51 code used for a single
24-bit read from the output register of the AD7712. Table VIII
shows some typical code for a single write operation to the con-
trol register of the AD7712. The 8XC51 outputs the LSB first
in a write operation while the AD7712 expects the MSB first, so
the data to be transmitted has to be rearranged before being
written to the output serial register. Similarly, the AD7712
outputs the MSB first during a read operation while the 8XC51
expects the LSB first. Therefore, the data that is read into the
serial buffer needs to be rearranged before the correct data-word
from the AD7712 is available in the accumulator.
WAIT:
READ:
POLL:
READ 1:
RLC A; MOV B.1,C; RLC A; MOV B.2,C;
RLC A; MOV B.3,C; RLC A; MOV B.4,C;
RLC A; MOV B.5,C; RLC A; MOV B.6,C;
RLC A; MOV B.7,C;
MOV A,B;
MOV @R0,A;
INC R0;
DEC R1
MOV A,R1
JZ END
JMP WAIT
END:
FIN:
MOV SCON,#00010001B; Configure 8051 for MODE 0
MOV IE,#00010000B;
SETB 90H;
SETB 91H;
SETB 93H;
MOV R1,#003H;
MOV R0,#030H;
MOV R6,#004H;
NOP;
MOV A,P1;
ANL A,R6;
JZ READ;
SJMP WAIT;
CLR 90H;
CLR 98H;
JB 98H, READ1
SJMP POLL
MOV A,SBUF;
RLC A;
MOV B.0,C;
SETB 90H
SJMP FIN
Table VII. 8XC51 Code for Reading from the AD7712
Operation
Disable All Interrupts
Set P1.0, Used as RFS
Set P1.1, Used as TFS
Set P1.3, Used as A0
Sets Number of Bytes to Be Read
in A Read Operation
Start Address for Where Bytes
Will Be Loaded
Use P1.2 as DRDY
Read Port 1
Mask Out All Bits Except DRDY
If Zero Read
Otherwise Keep Polling
Bring RFS Low
Clear Receive Flag
Tests Receive Interrupt Flag
Read Buffer
Rearrange Data
Reverse Order of Bits
Write Data to Memory
Increment Memory Location
Decrement Byte Counter
Jump if Zero
Fetch Next Byte
Bring RFS High
AD7712