use of basic I2C communication

[awsiuk]

Can anyone help me with using basic I2C functions from machine library? I'm trying to write a class for VEL6075 chip (https://datasheetspdf.com/pdf-file/1103874/Vishay/VEML6075/1). It has 16 bit registers where typical size register in many applications is 8bit. I'm limited to machine library. I came with this code

import machine
import time

SCL_PIN=machine.Pin(1)
SDA_PIN=machine.Pin(0)
i2c=machine.I2C(0,scl=SCL_PIN, sda=SDA_PIN,freq=400000)
buf=bytearray(2)
i2c.readfrom_mem_into(0x10, 0x0c, buf, addrsize=16)
print(buf[0], buf[1])

but it do not return 0x26 chip ID, but value 0x08. If i try to read 0x07 or 0x09 then i get 0x00. its not working. Ok, then i've tried:

VEL=machine.SoftI2C(scl=SCL_PIN, sda=SDA_PIN,freq=400000)

VEL.start()
x1=bytearray(1)
x1[0]=0x10 << 1 | 1

VEL.write(x1)
time.sleep(0.03)
VEL.write(bytes(0x0c))
time.sleep(0.03)
VEL.start()
VEL.write(bytes(0x10 << 1))
time.sleep(0.03)
b1=bytearray(1)
b2=bytearray(2)
VEL.readinto(b1)
VEL.readinto(b2)
VEL.stop()

But with this its even worse as b1 and b2 are 0xff. How to properly read 16bit registers? Or how to use properly "primitive" functions to get communication to I2C.
So how to read 16 bit registers properly or how to create proper communication using primitive functions like start, stop, write etc.

(Edit by @jimmo to add code formatting)

[jimmo]

Please see the welcome post for tips about code formatting.

Have you seen this driver? https://github.com/neliogodoi/MicroPython-VEML6075/blob/master/veml6075.py

[awsiuk]

Hello,

Thanks for reply and tips.
Yes, i've seen it and its not working for me. I get an error:

  Traceback (most recent call last):
  File "<stdin>", line 4, in <module>
  File "veml6075.py", line 52, in __init__
  File "veml6075.py", line 119, in _read_register
OSError: [Errno 5] EIO

I was also wondering whether this is correct:

unpack('BB', self._i2c.readfrom_mem(self._addr, register, 2))

as readfrom by default read 8 bits from register. Its states here read 2 bytes, but 2 bytes with 8 bit each.
I2C.readfrom_mem(addr, memaddr, nbytes, *, addrsize=8)
[((https://docs.micropython.org/en/latest/library/machine.I2C.html#machine.I2C.readfrom_mem))]
default address size is 8 bit.

To the shore.
I was trying to recreate protocol with primitive functions, but it seems they don't work for me. I was trying to read 16 bits, but it does not work for me either, but here probably because I wrongly initiate the sensor. This is where this code that you came was helping me to understand how functions work. I still don't know how they work for 16bit or how these primitive functions work.

[robert-hh]

OSError: [Errno 5] EIO is a fundamental communication error. That should be settled first. Either the I2C-Address is wrong, or the wiring, or pull-up resistors are missing. You can check the communication using i2c.scan(). The address list returned by is2.scan() must contain the address of your board.

[awsiuk]

ok, true... cables are not highest quality and had to check cables. It seems to work now. Thanks! Now it works as a charm.

I still have issues to understand that code. Can you explain how he reads 16 bit registers here?
self._i2c.readfrom_mem(self._addr, register, 2)
will read 2x8bit from 2 registers to my understanding. So if i will read 0x10 it will read 0x10 & 0x11. It will not grab 0x1000 register as a whole, unless i misunderstand the concept, meaning reading 2 bytes will continue reading from the same register as its simply 2 bytes long. My imagination tells me that it will read 2x8bit from 2 registers not from 1.