AD7705B interface to the BS2pe24

Andy McLeod

I have an application that will monitor pressure and temperature using the AD7705B ADC with the BS2pe. I have some code that was used with the 7706, but I can't seem to modify it successfully. Analog Devices provides a schematic to make this device, but is unfamiliar with the BS2, using instead some of their own microcontrollers as an example. Has anyone made this ADC work with the BS2/PBasic architecture?

Mohamed Refky

I think the connection is similar to AD7730

Here is the connection between AD7730 & BS2:
AD7730··················· BS2
(SCLK) pin1

---

pin12 (P7)···············CLOCK············
(DIN) pin22

---

pin13 (P8)················AD data input
(DOUT) pin21

---

pin14 (P9)············· AD data output
(RDY) pin20

---

pin15 (P10)············ Input pin number
You have DRDY instead of RDY
RESET => +5v
CS····· · => GND

Andy McLeod

Mohamed-

Thank you for that pinout. I'll try it with the code I have and see what it gives me.

Andy McLeod

Mohamed-

Do you have code for the 7730 that you would share with me?

Andy

Andy McLeod

Mohamed-

Using your prompt, I've come up with this code. It appears to work, thank you for the prompting!

' {$STAMP BS2pe}
' {$PBASIC 2.5}
'AD7705 BS2
'(SCLK) PIN1

---

PIN12 (P7) CLOCK
'(DIN) PIN14

---

PIN11 (P6) ADC DATA INPUT
'(DOUT) PIN13

---

PIN10 (P5) ADC DATA OUTPUT
'(DRDY) PIN12

---

PIN9 (P4) INPUT PIN number
'RESET

---

+5v
'CS

---

GND
'

---

Variables

---

sample VAR Word 'ADC reading
numsamples VAR Word 'Used to count samples in multiple instances
avg VAR Word(3) 'Temp variables for storing samples to be averaged
'

---

Constants

---

SCLK CON 7 'serial clock p7
DIN CON 5 'serial data in p5
DOUT CON 6 'serial data out p6
DRDY CON 4 'logic output p4

GOSUB initadc

avg = 0 ' Clear avg

'

---

Take 3 samples, at 60Hz intervals, and store in avg(0),avg(1),avg(2)

FOR numsamples = 0 TO 2
GOSUB getsample
PAUSE 17
avg(numsamples) = sample
NEXT

'

---

Calculate approximate average, preventing overflow

avg(0)=((avg(0)/3)+(avg(1)/3)+(avg(2)/3))
DEBUG "Avg=",DEC avg(0),CR ' Display the average value by sending over serial port

'

---

Subroutines

---

initadc:
SHIFTOUT 6,7,1,[noparse][[/noparse]%00100000] ' Configure a write to CLOCK register
SHIFTOUT 6,7,1,[noparse][[/noparse]%00001101] ' Master clock ENABLE, 4.9152 MHz config, 20 Samp/sec
SHIFTOUT 6,7,1,[noparse][[/noparse]%00010000] ' Configure a write to the SETUP register
SHIFTOUT 6,7,1,[noparse][[/noparse]%01000010] ' Self calibration, gain=1, bipolar buffered input
RETURN

getsample:
SHIFTOUT 6,7,0,[noparse][[/noparse]%00111000] ' Configure read from DATA register, 1st channel selected
SHIFTIN 5,7,0, [noparse][[/noparse]sample\16] ' Read in 16 bits, store in sample
RETURN

Mohamed Refky

Code for·AD7730

ADdata··· ·· var·· · WORD 'variable to hold 16 bit result.
DATAin···· con····· 2···········'AD data input pin.
DATAout· con·······3········· 'AD data output pin.
SCKL········· con····· 4········· 'clock to AD.
RDY·········· ·con····· 5········· 'RDY ·input .
INPUT 5
Initial:
SHIFTOUT DATAin, SCLK, MSBFIRST, [noparse][[/noparse]$FFFF\16,$FFFF\16] 'write 32 ones will reset the AD7730 to the default state
SHIFTOUT DATAin, SCLK, MSBFIRST, [noparse][[/noparse]$02] 'write to communication register setting next operation as write to mode register.
SHIFTOUT DATAin, SCLK, MSBFIRST, [noparse][[/noparse]$B0B0\16]'write to mode register initiating internal full scale calibration
pause 500
SHIFTOUT DATAin, SCLK, MSBFIRST, [noparse][[/noparse]$02]
SHIFTOUT DATAin, SCLK, MSBFIRST, [noparse][[/noparse]$B0B0\16]'write to mode register initiating system zero scale calibration
pause 500
SHIFTOUT DATAin, SCLK, MSBFIRST, [noparse][[/noparse]$3080\16] 'write to mode register starting continuous conversion for 10mV input range,unipolar,16 bit data word and 5V reference.
SHIFTOUT DATAin, SCLK, MSBFIRST, [noparse][[/noparse]$21] 'write to communication register setting next operation as continuous read from data register.
LOW 2 ' set DIN line low to insure part is not reset while in continuous read mode.
ReadData:
waitRDY:
IF RDY = 1 THEN waitRDY 'wait for RDY to go low to indicate output update.
SHIFTIN DATAout, SCLK, MSBPOST, [noparse][[/noparse]ADdata\16] 'read conversion result from data register.
DEBUG DEC ADdata, CR 'display data in decimal.
PAUSE 500 'wait 0.5 second between reading.
GOTO ReadData