ADS131M08: ADS131M08 HELP!! Configuration Issues - RASPBERRY PI 4b

Hi CELESTE GONZALE,

Can you please provide the following information?

1. Timing plots for SCLK, /CS, DIN, DOUT and /DRDY? for each register reading, the timing of two frames will be good because the register data will be shifted out in the 2nd frame.
2. Signal connections to your Raspberry Pi 4b.
3. Power supply connections.
4. Jumper configurations on the EVM.

The datasheet has a code example on page 93-94 that could be a reference for you.

Best regards,

Dale

Hello, good evening. I thank you for responding. I'm attaching my signals after the first capture. The enable signal is correct; I was only able to plot 4 signals, so I didn't include the enable signal in the graph, but I confirm that it's correct

Detail from +90us to +40us:

I'm only transmitting, and the responses are from the ADS. But after sending the data, I read the number of bytes I sent (described in detail from +2us to +5us)

Detail from +2us to +5us:

This is my current code; I implemented interrupts as in the example on pages 93-94 of the datasheet

CODE:

import spidev
import RPi.GPIO as GPIO
import time

class ads131m08():
# ADS131M08 commands
commands = {
'CMD_NULL': [0b00000000, 0b00000000], # Request ads samples
'CMD_RESET_DEVICE': [0b00000000, 0b00010001], # Reset the device
'CMD_STANDBY': [0b00000000, 0b00100010],
'CMD_WAKEUP': [0b00000000, 0b00110011],
'CMD_LOCK': [0b00000000, 0b10101010],
'CMD_UNLOCK': [0b00000000, 0b11001010],
'CMD_RREG': [0b10100000, 0b00000000], # Read register
'CMD_WREG': [0b01100000, 0b00000000], # Write register
}

def __init__(self, SyncResetGpio, DrdyGpio, DeviseSpi, cs, sclk=12000000):

# SPI configuration
self.spi = spidev.SpiDev()
self.spi.open(DeviseSpi, cs)
self.spi.max_speed_hz = sclk
self.spi.mode = 1
self.spi.lsbfirst = False # default

# ADS131M08 operates in mode 1
self.ChEnable = 8
self.DrdyGpio_init = DrdyGpio
# GPIO configuration
GPIO.setwarnings(False)
GPIO.setmode(GPIO.BCM)
GPIO.setup(9, GPIO.IN, pull_up_down=GPIO.PUD_DOWN) # pull down to eliminate noise issues

GPIO.setup(self.DrdyGpio_init, GPIO.IN) # To read the pin --> DrdyState = GPIO.input(DrdyGpio)

GPIO.setup(SyncResetGpio, GPIO.OUT) # To write the pin HIGH = Deactivate, LOW = Activate --> GPIO.output(SyncResetGpio, GPIO.LOW)
# GPIO.output(SyncResetGpio, GPIO.HIGH)
GPIO.setup(self.ChEnable, GPIO.OUT)

GPIO.output(SyncResetGpio, GPIO.LOW)

time.sleep(0.000125)

GPIO.output(SyncResetGpio, GPIO.HIGH)

def DrdyInterrup(self, channel):
"""if GPIO.input(self.DrdyGpio_init) == GPIO.LOW:"""
self.id()

def init_interrup(self):
# Initialize interrupt

GPIO.add_event_detect(self.DrdyGpio_init, GPIO.FALLING)
GPIO.add_event_callback(self.DrdyGpio_init, self.DrdyInterrup)

def cali(self):
tx_data = [0x00, 0x00, 0x00] # Data you want to send
self.spi.writebytes(tx_data)
tx_data = [0x00, 0x00, 0x00] # Data you want to send
self.spi.writebytes(tx_data)
tx_data = [0x00, 0x00, 0x00] # Data you want to send
self.spi.writebytes(tx_data)

def id(self):
# GPIO.output(self.ChEnable, GPIO.LOW)

# Adapt the signal.
adrress = 0x01 # ID, make this a parameter for a general read function.

tx_data = [0xA0, adrress, 0x00] # Data you want to send
self.spi.writebytes(tx_data)
self.spi.writebytes(tx_data)
self.spi.writebytes(tx_data)

rx_data = self.spi.readbytes(len(3 * tx_data)) # Read the same amount of bytes as you sent
# print("Received response:", rx_data)
# GPIO.output(self.ChEnable, GPIO.HIGH)

def close(self):
self.spi.close()

def invert(self):
pass
# print("Inverts the bits to use mode 3 as mode 1")

try:
ads = ads131m08(22, 24, 0, 0, 12000000)
ads.cali()
ads.init_interrup()
while True:
pass

except KeyboardInterrupt:
ads.close()
GPIO.cleanup()

CONNECTIONS:

Observing the schematic, I took the power input from 3v3_lp and connected it to the 3v3 power pin on the Raspberry Pi (pin 1). I connected GND to a ground pin on the Raspberry Pi (pin 39).

The following connections were made:

• SYNC/RESET to GPIO22
• DIN to GPIO10 - PIN 19
• DIGITAL.CLK - not connected
• CS to GPIO8 - PIN 24
• SCLK to GPIO11 - PIN 23
• DRDY to GPIO24 - PIN 18
• DOUT to GPIO9 - PIN 21
• GND - PIN 39
• VCC - PIN 1

To start, I didn't modify the ads131m08evm board. The default clock is 8192MHz. My initial goal is to read the registers correctly, following the datasheet to verify the data is accurate. Thank you very much for your assistance in advance. Regards

Hi CELESTE GONZALE,

It is not easy to check your timing. Below is a timing example captured on ADS131M04 for reading CFG register(0x06 address) which was already written 0x0700 to enable Global-chop mode with a default delay in the previous step. As you can see, the register data (0x0700) was successfully shifted out on DOUT line in the 2nd frame without checking and waiting for /DRDY signal.

Could you please show me your timing like this so that I can easily read the data? 

When you connect 3v3_lp on the EVM to the 3v3 power pin on your Raspberry Pi , dii you have a jumper on JP12 to short pin 1 and 2 of JP12? Also, did you provide any power to DVDD of the ADC on the EVM?

Regards,

Dale

Good afternoon! I'll detail the updates I've made. I modified my code to use only pigpio on my Raspberry Pi 4B in order to achieve a better clock and timing precision. I configured the SPI frequency to 2 MHz; I'm not certain if this frequency is correct. The datasheet specifies a maximum SPI clock frequency of 25 MHz, but it doesn't mention the minimum frequency. What is the known minimum frequency at which the ads131m08 can operate?

I'm using a simple 8-channel 25Ms/s logic analyzer. Due to this, I'm using a frequency of 2 MHz and I want to confirm if it's correct.

I edited my code to read the ID and STATUS registers, as well as to read all channels of the ads, implementing the timing described in this link: ADS131M08: DRDY not going low - Data converters forum - Data converters - TI E2E support forums

ADS131M08EVM Power Supply: I made the external power supply connection based on this note from the datasheet:

CÓDIGO: 

SECOND SAMPLE:

Temporal Timeline Graph - Reading STATUS Register

SECOND SAMPLE:

Temporal Graph Reading All ADC Channels

SECOND SAMPLE:

Hi CELESTE GONZALEZ CANTERO,

When your SCLK frequency is 2MHz, one clock period is 0.5us. If you want to read the data of all channels and your data size is 24 bits, one cycle has one STATUS word+8 channel data + CRC word, the minimum time for one cycle is (1+8+1)*24*0.5us=120us, so your data rate should be limited to 1/120us=8.3ksps (other delays are ignored).

It's very hard to see your timings except the 1st timing. Your command to read ID register is correct, your should be able to get the data of ID register in the 2nd frame, see my timings below that were just captured on the M08EVM. 0x2801 in the following 2nd frame is the data of ID register from M08 ADC.

1st frame to read ID register:

2nd frame to read ID register:

I could not clearly see your timing to read the STATUS register which has an address 01h, however it seems that your were sending 0xA001 command to the ADC, this is incorrect, the correct command is 0xA080. Please double check your command.

By the way, if the input CRC is disabled (default), you only need to send 24 SCLKs to read a register from the ADC instead of 48 SCLKs and also you only need to send NULL (all zeros) in the second sample/frame. See my timing in my previous post.

I could not see the details in your timing to read data of all channels, so I could not check it.

Best regards,

Dale