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Micropython I2C: i2c.writeto_mem(), in my code i get an error

0 votes
heres my code:
Code:
from machine import I2C import time print(" +-------------------------------------+") print(" | XBee MicroPython I2C Scanner Sample |") print(" +-------------------------------------+\n") # Instantiate an I2C peripheral. i2c = I2C(1) # Scan for I2C slaves connected to the interface and print their address. for address in i2c.scan(): print("- I2C device found at address: %s" % hex(address)) DEVICE = 0x20 # Device address (A0-A2) IODIRA = 0x00 # Pin direction register OLATA = 0x14 # Register for outputs GPIOA = 0x12 # Register for inputs # Set all GPA pins as outputs by setting # all bits of IODIRA register to 0 i2c.writeto_mem(DEVICE, IODIRA, 0x00) # Set output all 7 output bits to 0 i2c.writeto_mem(DEVICE, OLATA, 0) for MyData in range(1, 8): # Count from 1 to 8 which in binary will count # from 001 to 111 i2c.writeto_mem(DEVICE, OLATA, MyData) print(MyData) time.sleep(1) # Set all bits to zero i2c.writeto_mem(DEVICE, OLATA, 0)

The 3rd parameter in i2c.writeto_mem() tells me it should be a bytearray instead of a byte. what would a byte array look like? How would I pass in a bytearray that just contained sending a bit of value 1.

thanks
asked Jul 26 in MicroPython by edunn106 New to the Community (14 points)

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2 Answers

+1 vote
If you're getting that error on all writeto_mem() calls, you can do the following to create a valid object. It should work with either a "bytearray" or "bytes" object.
Code:
# build a 1-byte bytearray... buffer = bytearray(1) # ...and set the byte buffer[0] = 0x00 # create a bytes object of specific bytes buffer = bytes([0x00, 0xAA, 0x11]) # convert an integer buffer = chr(0xAA)

For setting bits, try this instead:
Code:
for bit in range(0, 8): # Set single bit of MyData MyData = chr(1 << bit) # or MyData = bytes([1 << bit]) i2c.writeto_mem(DEVICE, OLATA, MyData) print(MyData) time.sleep(1)

This should set bit 0, then bit 1, bit 2, etc.
answered Jul 28 by TomCollins Veteran of the Digi Community (1,833 points)
0 votes
I would suggest reading over http://cms.digi.com/resources/documentation/digidocs/90002219/#reference/r_class_i2c.htm?Highlight=I2C
answered Jul 27 by mvut Veteran of the Digi Community (12,786 points)
ok well now I have the right type of object passed through... the bytearray.

I have been using bytearray(b'\x00') and so forth. I dont quite understand the bytearray here. Is that one byte or one bit in the parenthesis. and if its a byte then how do I access its bits?
b'\x00' is a 1-byte array with a value of 0x00.  If "x = b'\x00'", you'd need to reference x[0] to get at that first byte, and then "x & 0x01" to check bit 0, "x & 0x80" to check bit 7, etc.
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