MAX1247 4-Channel, 12-Bit ADC

[Atom058]

I have scoured all of my resources and have come up with the following code but I seem to be missing something. Can anyone provide some insight?

' Set compiler to use HS (20 mHz)
@ DEVICE HS_OSC
DEFINE OSC 20 'resonator frequency at 20 Mhz

' Define the LCD Hookup parameters
' data pins D4-D7 are hooked to pins C.0-C.3, respectively
define LCD_DREG PORTC 'Data Port = PORTC
define LCD_DBIT 0 'Data starting bit = 0
define LCD_RSREG PORTC 'Register Select Port = PORTC
define LCD_RSBIT 4 'RS bit = PortC.4
define LCD_EREG PORTC 'Enable Port = PORTC
Define LCD_EBIT 5 'Enable Bit = PortC.5
define LCD_BITS 4 'LCD Bus Size = 4
define LCD_LINES 2 'Number of lines on LCD

define SHIFT_PAUSEUS 1000 '

Pause 1000 ' Wait for LCD to startup
Lcdout $FE, $80, "MAX1247"
lcdout $FE, $C0, "Example"
pause 1000

'Variables for ADC
CB var byte
CB0 var Byte
CB1 var Byte
CB2 var Byte
CB3 var Byte

ADResult var word ' contains the result of the read
X var byte ' counter

'Control Byte Setup:
' Bit 7: Start Bit = 1
' Bit 6: Channel Select Bit 2 (SEL2) -See Channel Selection Below
' Bit 5: SEL1
' Bit 4: SEL0
' Bit 3: UNI/BIP - 1=Unipolar 0=Bipolar
' Bit 2: SNGL/DIF - 1=Single Ended 0=Differential
' Bit 1: PD1 - Sets clock and power down mode
' Bit 0: PD0 - Sets clock and power down mode

'Channel Selection:
' SEL2 SEL1 SEL0
'CH0 0 0 1
'CH1 1 0 1
'CH2 0 1 0
'CH3 1 1 0

' To read channel 0 in Unipolar, single ended, external clock mode,
' Control Byte (CB) = 10011111
CB0 = %10011111 'To Read Channel 0
CB1 = %11011111 'To read channel 1
CB2 = %10101111 'To read Channel 2
CB3 = %11101111 'To read Channel 3

' Set up MAX1247 4-channel 12-bit ADC
CLKpin var PORTA.0 'SPI clock pin
CSpin var PORTA.1 'DAC chip select
DINpin var PORTA.2 'Data in pin
DOUTpin var PORTA.3 'Data Out Pin

'set up Max1247 pins
TRISA.0 = 0 'CLKpin as output
TRISA.1 = 0 'CSpin as output
TRISA.2 = 0 'DINpin as output
TRISA.3 = 1 'DOUTpin as input

'Take Reading
CB = CB0 'Read Channel 0
Loop:
CSpin = 1 'keep max1247 off until called
clkpin = 0 'keep clock low until ready

gosub ReadADC

Lcdout $FE, 1 ' Clear LCD screen

Lcdout $FE, $80, #ADresult

pause 330
goto loop

ReadADC:
'Send Control Byte
low CSpin 'cs going low starts the conversion process
shiftout doutpin, clkpin, 1, [cb\8]
high cspin
pause 10

'Read Result
adresult = 0
low cspin
shiftin dinpin, clkpin, 0, [adresult\12]
high cspin

return

end

[mister_e]

try..

ReadADC:
        'Send Control Byte
    low CSpin 'cs going low starts the conversion process
    shiftout doutpin, clkpin, 1, [cb\8]
        'Read Adc
    shiftin dinpin, clkpin, 0, [adresult\12]
    high cspin

    return

[Atom058]

Steve - Thanks for your reply (again). Unfortunately, the suggestion did not work. I have attached my board layout. It is pretty straight forward - Do you see anything I am missing? Ignore the other chip - it is a 12-bit D-A chip that works fine... Just can't get the input side of this to work. You will see that I have a pot supplying a voltage to CH0 of the MAX1247. I am trying to read this and display the result on the LCD.

Thanks!

[mister_e]

First observation, you have to disable ADCs on PORTA
ADCON1=7

and at the top, you should insert a short PAUSE (let's say 50) after
CSpin = 1
Just for safety sake


sorry i'm too lazy tonight to check the whole thing

Fortunately, someone else may have a deeper look to?

[Atom058]

Steve - I was really hoping that the ADCON1 thing was it as I missed that one, but still no go. I did the 50 mS pause you recommended, too.

I can't help but think this is one of those "can't see the forest through the trees" thing. I'm sure it's staring me right in the face. I am using a 12 bit D/A (4-channel) chip (MAX525) on this board as well and it works perfectly. Can't imagine why the A/D chip is giving me such a hard time...

Let me know if you think of anything else! Thanks!

[Atom058]

This is out of the data sheet for the MAX1247:

"the simplest software interface requires only
three 8-bit transfers to perform a conversion (one 8-bit
transfer to configure the ADC, and two more 8-bit transfers
to clock out the 12-bit conversion result)."

"Simple Software Interface
Make sure the CPU’s serial interface runs in master
mode so the CPU generates the serial clock. Choose a
clock frequency from 100kHz to 2MHz.

1) Set up the control byte for external clock mode and call it TB1. TB1 should be of the format: 1XXXXX11 binary, where the Xs denote the particular channel and conversion mode selected.

2) Use a general-purpose I/O line on the CPU to pull CS low.

3) Transmit TB1 and, simultaneously, receive a byte and call it RB1. Ignore RB1.

4) Transmit a byte of all zeros ($00 hex) and, simultaneously, receive byte RB2.

5) Transmit a byte of all zeros ($00 hex) and, simultaneously, receive byte RB3.

6) Pull CS high.

Figure 5 shows the timing for this sequence. Bytes RB2
and RB3 contain the result of the conversion, padded
with one leading zero and three trailing zeros. The total
conversion time is a function of the serial-clock frequency
and the amount of idle time between 8-bit
transfers. To avoid excessive T/H droop, make sure the
total conversion time does not exceed 120μs."

This seems to be telling me that I have to shift out 3 bytes (control, $00, $00) and I read back 3 bytes - the result is contained in the 2nd two bytes. It also mentions choosing a clock frequency of 100kHz to 2MHz. How do I do that?

I made a stab at the three out, three in routine but no result:

ReadADC:
low CSpin
shiftout doutpin, clkpin, 1, [cb] 'Send Control Byte
shiftin dinpin, clkpin, 0, [rb1] 'Read RB1 in and discard
shiftout doutpin, clkpin, 1, [$00] 'Send a byte of zeros
shiftin dinpin, clkpin, 0, [rb2] 'Read RB2
shiftout doutpin, clkpin, 1, [$00] 'Send a byte of zeros
shiftin dinpin, clkpin, 0, [rb3] 'Read RB3 - RB2&3 contain result
high cspin

return

Am I using the right modes for shiftin and out?