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Forum Index : Microcontroller and PC projects : Multiple I2C devices with MM2
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| LewW Newbie  Joined: 16/01/2018 Location: AustraliaPosts: 15 |
Hi all, I have noticed that none of the Silicon Chip MM2 projects use multiple IC2 devices. Specifically, I would like to add the DS3231 RTC to an altimeter using a BMP180. In fact, I would like to have an RTC in any device both to keep the time and display the time on any Backpack when it's not doing anything else. This especially comes into focus with the Backpack V3, which provides a home for a DS3231 on the main PCB. Is it possible to drive both the DS3231 and a sensor such as the BMP180? Does the native DS3231 support of the MM2 just hijack the I2C in such way that it cannot do anything else? Or is there perhaps some other limitation of the I2C implementation of the MM2? I have no doubt that anything is possible by bit banging, but I am not competent to do that sort of thing. I'm looking for things that can be done straightforwardly using MMBASIC commands. I would appreciate any clues you may be able to provide. I would not be all surprised if the answer is already on the Forum somewhere, but I have not been able to find it. Maybe I am over-thinking it, and I should just add the DS3231 to my altimeter and see if it works? Thankyou for reading this, Lew. Edited 2020-09-12 11:28 by LewW |
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TassyJim Guru  Joined: 07/08/2011 Location: AustraliaPosts: 6283 |
I2C devices have addresses. Provided that the addresses don't conflict, you can have as many devices as you wish on the one I2C port. Some devices have a select pin which allows you to change the address so you can have 2 of the same device on the one port. The DS3231has a different address to the BMP180 and BME280 so no problems. BMP085_Address = &H77 BME280_ADDRESS = &H76 DS3231_Address = &H68 On the micromites, if you use the built-in RTC commands, the RTC is only interrogated at startup then the timekeeping is done by the CPU. You don't have to use the built-in RTC commands. You could roll your own if you want to do more than the standard offering. I have one configured as an alarm clock, starting the micromite at a preset time then putting it to sleep when the work is done. Jim VK7JH MMedit |
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| DaveC166 Regular Member  Joined: 13/09/2012 Location: New ZealandPosts: 44 |
There is allso the option of using a second I2C port. This is done with a C Function. I had to use this option because HTU21D temp/humidity sensor modules, I2C address is not changeable. I used two HTU21D's on one MK2 umite.The C function is part of the firmware download and works fine as long as you have 3 spare digitals pins. |
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| LewW Newbie Joined: 16/01/2018 Location: AustraliaPosts: 15 |
Hi Jim, Thankyou very much for your very quick and helpful reply. This has been bothering me for quite a while. I should have posted my question years ago! I knew that I2C could accommodate multiple devices via their addresses, but since I had never seen any one use two devices with a MM, I thought the MM implementation might have been limited. It seems that I did GeoffG a disservice. Sorry Geoff! OK, I will just try it. I usually update the time from the RTC every 10 minutes as in the SuperClock, so it will be addressed regularly. (I also borrow the SuperClockFonts, which are great!) I probably should try rolling my own I2C commands for the DS3231 - it might be a good way to start growing my skills. The most ambitious thing I have done so far is just to get the temperature out of it using RTC commands. Thanks again Jim, Lew. (VK2ZIP) |
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| LewW Newbie Joined: 16/01/2018 Location: AustraliaPosts: 15 |
Hi Dave, Thanks to you also for your reply. I have now found that C function in my last download. I think I was aware of it at the time, and that possibly contributed to my impression that the native I2C on the MM2 was limited. I had not thought of the issue of needing to drive two devices with the same hard-wired addresses. It is good to get that all into perspective, but I do have one question. You mentioned the need for 3 digital pins. The need for two is obvious to me, but what is the third pin used for? Lew. |
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CaptainBoing Guru Joined: 07/09/2016 Location: United KingdomPosts: 2170 |
same meat, different gravy. A DS3231 and HTU21D happily co-habiting.  As already pointed out, each device has an address and will ignore traffic not for it's own address. |
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IanT Senior Member  Joined: 29/11/2016 Location: United KingdomPosts: 108 |
Hi Lew, First the disclaimer - I'm learning this stuff too (and have been for some time I'm afraid) - so I'm not a Guru. I have a different problem with I2C which involves controlling four I2C slave devices (from a single 170) that share a single unique (e.g. fixed) I2C address. Everything was put on hold for a while, as I puzzled how best to get around this issue but then I discovered I could possibly use an I2C multiplex switch. I think this should work in my case and I've just ordered some small PCBs that have this chip pre-mounted. This chip is the TI TCA9548A (Low-Voltage 8-Channel I2C Switch) and I think I should be able to hook up my BDLC chips to the MM using one of them. We'll see once I get to actually try it. Anyway - I thought it was worth mentioning that this I2C switch exists and might be helpful in solving some I2C device address problems/conflicts. Regards, IanT (MMB White Belt) |
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| DaveC166 Regular Member Joined: 13/09/2012 Location: New ZealandPosts: 44 |
Sorrt Lew, that was a typo, only two digital pins are needed for the second I2c port |
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| Volhout Guru Joined: 05/03/2018 Location: NetherlandsPosts: 5089 |
Not exactly demo code, but this program reads temperature and humidity from a TI sensor, (I2C) and stores it in EEPROM (I2C). code PicomiteVGA PETSCII ROBOTS |
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