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PicŪ Basic
The codes have been developed for reading/writing operation to the Analog Device AD7705 and Maxim MX7705 (not MAX7705:it is a different chip) 16 bit Sigma Delta AD converter with on chip digital filter and programmable gain amplifier. The AD7705 is a very good analog to digital converter but the output data rate is limited to 500Hz.
The AD7705 and MX7705 are pin to pin compatible.
Datasheet for AD7705. Attach:AD7705.pdf
Datasheet for MX7705. Attach:MX7705.pdf
The reset pin has been tied to VCC (+5V) with 4k7 resistor. The device can be reset connecting this pin to GND or via software.
The DRDY pin is the device ready flag. When DRDY is set to +5V then the device is busy. The Ready flag can be checked also via software reading the first MSB bit of the communication register. If the bit is set to 1 then the 7705 is busy.
Pin 10 and 9 are for the external voltage reference. I have used the MicroChip MCP1525 in TO92 package. This chip is set to 2.5V.
I used the 7705 in one channel unipolar mode. So I tied the AN1- pin (pin 8) to GND. AN1+ pin (pin 7) was connected to a potentiometer.
Pin 1 is the serial clock input pin while pin 4 is the Chip Select Pin. When CS is 0, the device is selected. This pin can be connected to GND if only one device is used on the serial bus.
In pin 14 (DIN) a serial data is sent from PICŪ while pin 13 (DOUT) is the output from the 7705 to uC. To save PICŪ pins these ports can be connected together using a 4k7 pull up (to VCC) resistor. See datasheet for connection hints.
The PICŪ pins configuration for MX7705_GLCD.bas code are described with the following definitions:
Code:
Symbol SCK=PORTA.5 'Clock pin
Symbol SI=PORTA.3 ' AD7705 Data in pin
Symbol SO=PORTA.2 ' AD7705 Data out pin
Symbol CS = PORTA.4 'AD7705 Chip Select pin
Symbol ready=PORTA.1 'AD7705 Ready pin
For this code the definitions are:
Symbol SCK=PORTA.5 'Clock pin
Symbol SI=PORTA.2 ' AD7705 Data in pin
Symbol SO=PORTA.2 ' AD7705 Data out pin. Is the same pin of SI
Symbol SI=PORTA.2 ' AD7705 Data in pin
Symbol SO=PORTA.2 ' AD7705 Data out pin. Is the same pin of SI
The following picture shows how I made the connection to AD7705 using Proton Board and 16F877 running @ 4Mhz. In this picture the AD7705 channel 1 was connected to a potentiometer. On the GLCD are shown the AD converter word value (21922), the AD value in 16 bit format and the scaled value in volts format.
Thanks to GLCD and Proton basic, it is very easy to plot the voltage trend.
The two wires connection is shown below. Note the pull up resistor connected to 7705 pin 13 and the jumper between pin 13 and pin 14. CS signal from PICŪ is not present (CS connected to GND). The Ready pin of 7705 is still connected to PICŪ but is not used. The ready flag is checked via serial interface.
The software is divided into two sections. The first section is for 7705 set-up. In fact at power-up or after a reset the 7705 waits for set-up configuration commands from the uC. The channel, the clock source and the operating mode are selected writing to three registers:the communication, the clock and the set-up registers. For writing operation two bytes must be sent. The first one is always sent to communication register and it is used for register (for example clock or set-up register) and operation (write/read) selection. The byte is also used to select the conversion channels and if it is required a read or write mode to the selected register. The second byte is the command sent to the register selected in the first byte. The 7705 always expects bytes in MSB format.
Example:
First byte: Send=$20 ' send command $20 to communication register. $20 hex is 00100000 in binary format. Look at the communication register in the table below.
Lets analysize the byte 00100000
DRDY bit set to 0: this bit must be set to 0 for write operation. During read operation it indicates if the device in ready (0)/busy(1) condition.
RS2-1-0:register selection. 010 select the clock register.
R/W: set to 0 for write operation. Set to 1 for read operation. In this example is set to 0 because we are sending a write command to the clock register (selected with RS2-1-0 bits).
STBY:set to 1 to put the device in power save mode. Set to 0 for normal operation.
CH1-0: channel selection. Set to 00 to select channel 1.
Second byte: rec=$C 'write on clock register': clock division=1, clock bit=1, master clock enabled (bit set to 0), bit output rate set to 50hz (maximum is 500Hz). The binary code is 00001100. See clock register table below. Note that in MX7705 the table has the first bit set always to 1 (is the Maxim identification) also if you sent a 0 bit.
For reading operation one byte is sent from the PICŪ to the communication register. The byte includes the register to be read and the R/W bit always set to 1. After the command is sent, the 7705 send back to the PICŪ a byte or word with the requested information.
The below picture shows the timing diagrams for read and write operation.
The second part of the software is free running conversion with trend plot.
The code for read/write operation is the following (related to 5 pin interface. The two wires code is very similar. Only CS command are no more present):
AD_write:
'AD7705 write routine
'first byte is for channel selection and register selection (R/W bit is set to 0)
'second byte is the value to be sent
'this routine is valid only for 8 bit register as communication,clock and set-up register.
Low CS ' Enable device
SHOut SI, SCK, msbfirst, [Send\8] ' Send command to communication register
SHOut SI, SCK, msbfirst, [rec\8] ' Send value to the selecte register
High CS ' Disable device
Print At 2,1,"Send:",HEX Send," Dat:",HEX rec," " 'print command
Return
AD_read:
'Read from AD7705
'first byte is the register address (R/W bit is set to 1)
'second byte is register content
Low CS 'Enable device
SHOut SI, SCK, msbfirst, [Send\8] 'Send read command and address
SHIn SO, SCK, msbpre, [rec\8] ' Read data
High CS ' Disable device
Print At 3,1,"Rec:",HEX Send," Dat:",HEX rec," "
Return
AD_read2:
'Read AD7705 conversion result
'A 16 bit value is expected
Low CS 'Enable device
SHOut SI, SCK, msbfirst, [Send\8] ' Send read command and data register address
SHIn SO, SCK, msbpre, [ad\16] ' Read 16 bit data
High CS ' Disable device
Print At 0,1,"Rec:",HEX Send," AD:",Dec ad," "
Print At 1,1,"Ad:",BIN ad
value= (ad*2.5)/65535
Print At 2,1,"Volts:",DEC8 value," "
Return
The Ad_Read2 subroutine is for reading the converted value (a word value) while the Ad_read subroutine is for register reading.
The 7705 Ads have many features not described in this short page. My code is just a kick start code that I hope can save you some time. If you have any question you can send me an email.
Two codes are provided.
The first one is MX7705_GLCD.bas and it uses 5 PICŪ pins (CS,SI,SO,Ready,SCLK).
Code:
'****************************************************************
'* Name : MX7705 16f877.BAS *
'* Author : Marco D'Onofrio *
'* Notice : Copyright (c) 2004 Donomark *
'* : All Rights Reserved *
'* Date : 26/11/2004 *
'* Version : 1.0 *
'* Notes : version with 16f877,GLCD and trend plot *
'* : Code working properly. *
'****************************************************************
Include "PROTON_G4.INT"
' Demo software for AD7705 (Analog device) and Maxim MX7705 (the chips are pin to pin compatible) 16 bits Sigma delta AD converter with digital filtering
' In this demo 5 PICŪ pins are used. However it is possible to reduce the line to two (Cs connected to GND, ready flasg
' read from register and not from pin, SI and SO pin tied togheter with a pull-up resistor. See AD7705 or MX7705 datasheet
' Draw a scale with X and Y lines
' Incremental tick marks are also added
' Using a GRAPHIC LCD with an external FONT
Symbol SCK=PORTA.5 'Clock pin
Symbol SI=PORTA.3 ' AD7705 Data in pin
Symbol SO=PORTA.2 ' AD7705 Data out pin
Symbol CS = PORTA.4 'AD7705 Chip Select pin
Symbol ready=PORTA.1 'AD7705 Ready pin
'Variables for scale drawing (the code for scale drawing is from Proton demo file)
Dim S_XSTART As Byte
Dim S_XEND As Byte
Dim S_YSTART As Byte
Dim S_YEND As Byte
Dim S_YTICK As Byte
Dim S_XTICK As Byte
Dim XPOS As Byte
Dim YPOS As Byte
Dim time_unit As Byte 'variable used for ascissa
Dim Send As Byte 'byte sent to communication register of AD7705
Dim rec As Byte 'byte received from AD7705:only for communication register, set-up register and clock register (8 bit registers)
Dim I As Byte 'general purpose variable
Dim ad As Word 'ad converter value read from AD7705
Dim value As Float 'variable used for Y drawing
Dim value_old As Float 'previous value
Clear 'clear all variables
Cls 'clear LCD
S_XSTART = 0 ' XPOS start position
S_XEND = 119 ' XPOS end position
S_YSTART = 0 ' YPOS start position
S_YEND = 59 ' YPOS end position
S_XTICK = 10 ' X increment of TICKS
S_YTICK = 10 ' Y increment of TICKS
start:
Print At 0,1,"Mx7705 AD Config"
DelayMS 250
Send=$20 ' send command $20 to communication register: channel 1 selected, next operation is a write on clock register
rec=$C 'write on clock register: clock division=1, clock bit=1, master clock enabled (bit set to 0), bit output rate set to 50hz (maximum is 500Hz)
GoSub AD_write 'call the subroutine for AD write
Send=$28 'send command to communication register:next operation is a read from clock register to check if previous command succeded
GoSub AD_read
calib: 'self-calibration
Send=$10 ' send command to communication register:channel 1 selected, next operation is a write on set-up register
rec=$46 ' write $46 (bin 01000110) on set-up register:enable self calibration,gain 1, unipolar operation, buffer control on, enable filter synchronization
'note that after the self calibration, AD7705 start free conversion cycle
GoSub AD_write 'send command to AD7705
Send=$18 'read back to check command has been accepted
GoSub AD_read
While ready=1 'check if ready pin is low. If low AD7705 is ready for next operation
Print At 4,1,"wait"
High PORTD.0
Wend
DelayMS 100
Low PORTD.0
'AD7705 set-up finished. Start conversions
Cls 'clear LCD
GoSub Draw_Scale' Draw the scale
loop:
Send=$38 'send command to communication register:next operation is reading the 16bit data register where conversion result are stored
GoSub AD_read2
While ready=1 'wait AD7705 until the conversion is finished
Print At 4,1,"wait"
Wend
Inc time_unit ' draw the trend
Line 1,time_unit-1,(60-value_old*10), time_unit,(60-value*10)
If time_unit=119 Then 'if time unit is 119, clear GLCD and start again
Cls
GoSub Draw_Scale ' Draw the scale
Clear time_unit
EndIf
value_old=value
If InKey=0 Then GoTo calib 'if SW1 is pressed, perform self-calibration and starts againg conversion
If InKey=1 Then 'if SW2 is pressed, put PICŪ in pause mode
Snooze 5
While InKey=16
Snooze 5
Wend
EndIf
GoTo loop
AD_write:
'AD7705 write routine
'first byte is for channel selection and register selection (R/W bit is set to 0)
'second byte is the value to be sent
'this routine is valid only for 8 bit register as communication,clock and set-up register.
Low CS ' Enable serial Dac
SHOut SI, SCK, msbfirst, [Send\8] ' Send write enable command
SHOut SI, SCK, msbfirst, [rec\8] ' Send write enable command
High CS ' Disable to execute command
Print At 2,1,"Send:",HEX Send," Dat:",HEX rec," " 'print command
Return
AD_read:
'Read from AD7705
'first byte is the register address (R/W bit is set to 1)
'second byte is register content
Low CS
SHOut SI, SCK, msbfirst, [Send\8] ' Send read command and address
SHIn SO, SCK, msbpre, [rec\8] ' Read data
High CS ' Disable
Print At 3,1,"Rec:",HEX Send," Dat:",HEX rec," "
Return
AD_read2:
'Read AD7705 conversion result
'A 16 bit value is expected
Low CS
SHOut SI, SCK, msbfirst, [Send\8] ' Send read command and address
SHIn SO, SCK, msbpre, [ad\16] ' Read 16 bit data
High CS ' Disable
Print At 0,1,"Rec:",HEX Send," AD:",Dec ad," "
Print At 1,1,"Ad:",BIN ad
value= (ad*2.5)/65535
Print At 2,1,"Volts:",DEC8 value," "
Return
'---------------------------------------------------------------------------
' Draw_Scale subroutine which draws an XY scale with tick marks
' Assumes values assigned to S_XPOS,S_YPOS,S_XTICK,X_XEND,S_YEND and S_YTICK
Draw_Scale:
' Draw vertical Y axis
I = 0
YPOS = S_YSTART
Repeat
Plot YPOS,S_XSTART
Inc I
Inc YPOS
Until YPOS > S_YEND
' Add the tick marks to the Y axis
YPOS = S_YSTART
Repeat
Plot YPOS,S_XSTART + 1
YPOS = YPOS + S_YTICK
Until YPOS > S_YEND
' Draw horizontal X axis
XPOS = S_XSTART
Repeat
Plot S_YEND,XPOS
Inc XPOS
Until XPOS > S_XEND
' Draw X axis tick marks
XPOS = S_XSTART
Repeat
Plot S_YEND - 1,XPOS
XPOS = XPOS + S_XTICK
Until XPOS > S_XEND
Return
Include "FONT.INC"
Code:
'****************************************************************
'* Name : MX7705 GLCD 2 WIRES *
'* Author : Marco D'Onofrio *
'* Notice : Copyright (c) 2004 Donomark *
'* : All Rights Reserved *
'* Date : 10/12/2004 *
'* Version : 1.0 *
'* Notes : version with 16f877,GLCD and trend plot *
'* : 2 wires interface with serial ready flag reading *
'****************************************************************
Include "PROTON_G4.INT"
' Demo software for AD7705 (Analog device) and Maxim MX7705 (the chips are pin to pin compatible) 16 bits Sigma delta AD converter with digital filtering
' In this demo 2 PICŪ pins are used. Cs is connected to GND, ready flag is read via serial line
' SI and SO pin are tied togheter with a 4k7 resistor pull-up resistor to VCC. See AD7705 or MX7705 datasheet
' Only Si/SO pin a clock pin are used
' Draw a scale with X and Y lines
' Incremental tick marks are also added
' Code working properly
' Using a GRAPHIC LCD with an external FONT
Symbol SCK=PORTA.5 'Clock pin
Symbol SI=PORTA.2 ' AD7705 Data in pin
Symbol SO=PORTA.2 ' AD7705 Data out pin. Is the same pin of SI
'Variables for scale drawing (the code for scale drawing is from Proton demo file)
Dim S_XSTART As Byte
Dim S_XEND As Byte
Dim S_YSTART As Byte
Dim S_YEND As Byte
Dim S_YTICK As Byte
Dim S_XTICK As Byte
Dim XPOS As Byte
Dim YPOS As Byte
Dim time_unit As Byte 'variable used for ascissa
Dim Send As Byte 'byte sent to communication register of AD7705
Dim rec As Byte 'byte received from AD7705:only for communication register, set-up register and clock register (8 bit registers)
Dim ready As Byte 'AD7705 Ready BIT
Dim I As Byte 'general purpose variable
Dim ad As Word 'ad converter value read from AD7705
Dim value As Float 'variable used for Y drawing
Dim value_old As Float 'previous value
Clear 'clear all variables
Cls 'clear LCD
S_XSTART = 0 ' XPOS start position
S_XEND = 119 ' XPOS end position
S_YSTART = 0 ' YPOS start position
S_YEND = 59 ' YPOS end position
S_XTICK = 10 ' X increment of TICKS
S_YTICK = 10 ' Y increment of TICKS
start:
Print At 0,1,"Mx7705 AD Config"
DelayMS 250
Send=$20 ' send command $20 to communication register: channel 1 selected, next operation is a write on clock register
rec=$C 'write on clock register: clock division=1, clock bit=1, master clock enabled (bit set to 0), bit output rate set to 50hz (maximum is 500Hz)
GoSub AD_write 'call the subroutine for AD write
Send=$28 'send command to communication register:next operation is a read from clock register to check if previous command succeded
GoSub AD_read
calib: 'self-calibration
Send=$10 ' send command to communication register:channel 1 selected, next operation is a write on set-up register
rec=$46 ' write $46 (bin 01000110) on set-up register:enable self calibration,gain 1, unipolar operation, buffer control on, enable filter synchronization
'note that after the self calibration, AD7705 start free conversion cycle
GoSub AD_write 'send command to AD7705
Send=$18 'read back to check command has been accepted
GoSub AD_read
Send=$8 'send read request to communication register
GoSub AD_read
ready=rec & %10000000 'check if the MSB BIT is =1
While ready=%10000000 'If MSB bit (bit 8) is 1 AD7705 is busy
Print At 4,1,"wait" 'Wait until ready bit is 0
High PORTD.0
GoSub AD_read
ready=rec & %10000000
Wend
DelayMS 100
Low PORTD.0
'AD7705 set-up finished. Start conversions
Cls 'clear LCD
GoSub Draw_Scale' Draw the scale
loop:
Send=$38 'send command to communication register:next operation is reading the 16bit data register where conversion result are stored
GoSub AD_read2
Send=$8 'send read request to communication register
GoSub AD_read
ready=rec & %10000000 'check if the MSB BIT is =1
While ready=%10000000 'wait AD7705 until the conversion is finished
Print At 4,1,"wait"
High PORTD.0
GoSub AD_read
ready=rec & %10000000
Wend
Inc time_unit ' draw the trend
Line 1,time_unit-1,(60-value_old*10), time_unit,(60-value*10)
If time_unit=119 Then 'if time unit is 119, clear GLCD and start again
Cls
GoSub Draw_Scale ' Draw the scale
Clear time_unit
EndIf
value_old=value
If InKey=0 Then GoTo calib 'if SW1 is pressed, perform self-calibration and starts againg conversion
If InKey=1 Then 'if SW2 is pressed, put PICŪ in pause mode
Snooze 5
While InKey=16
Snooze 5
Wend
EndIf
GoTo loop
AD_write:
'AD7705 write routine
'first byte is for channel selection and register selection (R/W bit is set to 0)
'second byte is the value to be sent
'this routine is valid only for 8 bit register as communication,clock and set-up register.
SHOut SI, SCK, msbfirst, [Send\8] ' Send command to communication register
SHOut SI, SCK, msbfirst, [rec\8] ' Send value to the selecte register
Print At 2,1,"Send:",HEX Send," Dat:",HEX rec," " 'print command
Return
AD_read:
'Read from AD7705
'first byte is the register address (R/W bit is set to 1)
'second byte is register content
SHOut SI, SCK, msbfirst, [Send\8] 'Send read command and address
SHIn SO, SCK, msbpre, [rec\8] ' Read data
Print At 3,1,"Rec:",HEX Send," Dat:",HEX rec," "
Return
AD_read2:
'Read AD7705 conversion result
'A 16 bit value is expected
SHOut SI, SCK, msbfirst, [Send\8] ' Send read command and data register address
SHIn SO, SCK, msbpre, [ad\16] ' Read 16 bit data
Print At 0,1,"Rec:",HEX Send," AD:",Dec ad," "
Print At 1,1,"Ad:",BIN ad
value= (ad*2.5)/65535
Print At 2,1,"Volts:",DEC8 value," "
Return
'---------------------------------------------------------------------------
' Draw_Scale subroutine which draws an XY scale with tick marks
' Assumes values assigned to S_XPOS,S_YPOS,S_XTICK,X_XEND,S_YEND and S_YTICK
Draw_Scale:
' Draw vertical Y axis
I = 0
YPOS = S_YSTART
Repeat
Plot YPOS,S_XSTART
Inc I
Inc YPOS
Until YPOS > S_YEND
' Add the tick marks to the Y axis
YPOS = S_YSTART
Repeat
Plot YPOS,S_XSTART + 1
YPOS = YPOS + S_YTICK
Until YPOS > S_YEND
' Draw horizontal X axis
XPOS = S_XSTART
Repeat
Plot S_YEND,XPOS
Inc XPOS
Until XPOS > S_XEND
' Draw X axis tick marks
XPOS = S_XSTART
Repeat
Plot S_YEND - 1,XPOS
XPOS = XPOS + S_XTICK
Until XPOS > S_XEND
Return
Include "FONT.INC"
Using PDS with SPI GLCD based on ST7565R Controller
Graphic LCDs based on the ST7565 are cheaper then GLCDs with other controllers. SPI requires only four pins. If the circuit