2
REV.G
AD7711
–25–
START
WRITE DATA FROM
ACCUMULATOR TO
SERIAL BUFFER
BRING
TFS AND A0 LOW
LOAD DATA FROM
ADDRESS TO
ACCUMULATOR
CONFIGURE AND
INITIALIZE
C/ P
SERIAL PORT
BRING
RFS, TFS AND
A0 HIGH
BRING
TFS AND A0 HIGH
END
3
REVERSE
ORDER OF
BITS
Figure 16. Flowchart for Single Write Operation
to the AD7711
AD7711 to 8051 Interface
Figure 17 shows an interface between the AD7711 and the 8XC51
microcontroller. The AD7711 is configured for external clocking
mode, while the 8XC51 is configured in its Mode 0 serial interface
mode. The
DRDY line from the AD7711 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.
P1.0
P3.0
P3.1
P1.1
P1.2
P1.3
8XC51
AD7711
SDATA
A0
RFS
TFS
MODE
DRDY
SYNC
SCLK
DVDD
Figure 17. AD7711 to 8XC51 Interface
Table VII shows some typical 8XC51 code used for a single 24-bit
read from the output register of the AD7711. Table VIII shows
some typical code for a single write operation to the control
register of the AD7711. The 8XC51 outputs the LSB first in a
write operation, while the AD7711 expects the MSB first so the
data to be transmitted has to be rearranged before being written
to the output serial register. Similarly, the AD7711 outputs the
MSB first during a read operation that 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
AD7711 is available in the accumulator.
Table VII. 8XC51 Code for Reading from the AD7711
MOV SCON,#00010001B;
Configure 8051 for MODE 0
MOV IE,#00010000B;
Disable All Interrupts
SETB 90H;
Set P1.0, Used as
RFS
SETB 91H;
Set P1.1, Used as
TFS
SETB 93H;
Set P1.3, Used as A0
MOV R1,#003H;
Sets Number of Bytes to Be Read in
Read Operation
MOV R0,#030H;
Start Address for where Bytes Will
Be Loaded
MOV R6,#004H;
Use P1.2 as
DRDY
WAIT:
NOP;
MOV A,P1;
Read Port 1
ANL A,R6;
Mask Out All Bits Except
DRDY
JZ READ;
If Zero Read
SJMP WAIT;
Otherwise Keep Polling
READ:
CLR 90H;
Bring
RFS Low
CLR 98H;
Clear Receive Flag
POLL:
JB 98H, READ1
Tests Receive Interrupt Flag
SJMP POLL
READ 1:
MOV A,SBUF;
Read Buffer
RLC A;
Rearrange Data
MOV B.0,C;
Reverse Order of Bits
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;
Write Data to Memory
INC R0;
Increment Memory Location
DEC R1
Decrement Byte Counter
MOV A,R1
JZ END
Jump if Zero
JMP WAIT
Fetch Next Byte
END:
SETB 90H
Bring
RFS High
FIN:
SJMP FIN