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Forum Index : Microcontroller and PC projects : Micromite I2C 16 Bit Read / Write
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| kg4pid Regular Member  Joined: 08/03/2015 Location: United StatesPosts: 50 |
I have been slowly working on building my own weather station and wanted to use a standard Micromite to read a few sensors and send that data via rf to a reciever inside for further processing. One of the sensors is a Vishay VEML6075 UV sensor and it has a I2C interface. It uses registers that are 16 bits wide instead of 8 bits and requires 16 bit transfers. Here is the data sheet... Vishay VEML6075 At the top of page 6 it says "Each of the registers in the VEML6075 are 16 bit wide, so 16 bit should be written when a write command is sent, and 16 bit should be read when a read command is sent." Using a raspberry pi and python I was able to use bus.write_word_data and bus.read_word_data to do the 16 bit read and write. What I need to know is if the micromite can do 16 bit I2c read and write since I would like to use it to read my sensors. The VEML6075 is the only one that uses 16 bits instead of 8. I don't currently own a micromite so I can't test anything. Thanks Max |
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| Phil23 Guru  Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
Hi, Page 85 talks about it. Seems you specify the number of Bytes to be written or read. The Example there Writes 3 bytes, [code]I2C WRITE &H6F, 1, 3, &H23, &H43, &H25[/code] If it was only to write 2 bytes, or 16 bits it would be, [code]I2C WRITE &H6F, 1, 2, &H23, &H43[/code] or [code]I2C WRITE &H6F, 1, 2, &B00100011, &B01000011[/code] Correct me if I have the Hex to Bin wrong. Phil. |
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| kg4pid Regular Member Joined: 08/03/2015 Location: United StatesPosts: 50 |
Not the same thing. This sensor uses 16 bit transfers or words. Your example uses 8 bit transfers or bytes. Max |
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Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9081 |
You might need a 16-bit Cfunction to deal with that. Matherp or Geoff would be able to say for sure. MOST I2C stuff is 8-bit, so this device is being difficult.  I would have thought that even if it DOES need to send 16-bits, it would send a two-byte word rather then a 16-bit word, as just about everything can deal with 8-bit I2C....  Smoke makes things work. When the smoke gets out, it stops! |
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KeepIS Guru Joined: 13/10/2014 Location: AustraliaPosts: 1399 |
I must be reading the data sheet incorrectly. It has 16 bit resolution and holding registers, in the timing diagrams 16 bit transfers appear to be normal HI - LO bytes transfers. Which is the norm for R/W 16 bit values in most sensors. Once again, excuse my ignorance if I'm reading that wrong. Mike. It's all too hard. Mike. |
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| kg4pid Regular Member Joined: 08/03/2015 Location: United StatesPosts: 50 |
Vishay has to be different than everyone else! Their VELM6070 used two addresses, which is again unusual, but at least it used 8 bit transfers. But it doesn't do all the things that the VELM6075 does. I wanted to just use a simple PICF88 but can't find any 16 bit I2C routines for that either. So that is why I was going to try the micromite in hopes it could do it without reinventing the wheel. |
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GoodToGo! Senior Member  Joined: 23/04/2017 Location: AustraliaPosts: 188 |
Reading the datasheet shows that the data is sent/read in Low byte/High byte format to make up the 16bit word. Or in other words, 2x 8 bit transfers, not 1 x 16 bit transfer. The MM should do it fine, and although I haven't tested it, Phil's code should be ok. Cheers! GTG!  ...... Don't worry mate, it'll be GoodToGo! |
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| kg4pid Regular Member Joined: 08/03/2015 Location: United StatesPosts: 50 |
I sure hope the micromite can do this without any problems. When I was writing the code on the raspberry pi and python all I got was errors until I started using the bus.write_word_data and bus.read_word_data commands. I've never had to do that before but then again I might not know what I'm doing.  |
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TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 5923 |
The data sheet shows the data being sent in 2 8bit bytes with the ACK between them.  All they want is for you to read/write both high and low bytes at the same time. Jim VK7JH MMedit MMBasic Help |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9081 |
...and there you have it. Smoke makes things work. When the smoke gets out, it stops! |
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| kg4pid Regular Member Joined: 08/03/2015 Location: United StatesPosts: 50 |
I rewrote the code to read the raw data and have it working, so the micromite should be able to do it to. Now if I can just figure out how to finish the code to calicate the UV index. My brain is tired. Thanks for all the help, Max |
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