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Forum Index : Microcontroller and PC projects : Micromite Master / Slave
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halldave Senior Member  Joined: 04/05/2014 Location: AustraliaPosts: 121 |
Can I use 3 Micromites, 1 of them the master, communicating to two slaves communicating through the COM1: and COM2: on the Master, as I want to use the i2c for Real Time Clock on the master The idea is I will have 17 ports available on Slave 1 17 ports available on Slave 2 and 15 ports available on master Each of the slaves will control 8 Zone alarm I/O (with Zone doubling to 16) The master will interface with keypad, RTC, LCD, Ethernet, 2 x relays Is anyone else working on Home Security, i'm happy to share my eagle schematics regards David |
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TassyJim Guru  Joined: 07/08/2011 Location: AustraliaPosts: 6103 |
If you want to multidrop the serial lines, you will need to run the slaves with the 'OC' option and a pullup resistor to allow all 3 slaves share the 'reply' bus. The master TX can be connected to the 3 slave Rx pins without any difficulty. Even with the RTC on the master, you can easily run the 3 slaves off the I2C. Just give them different addresses. The RTC doesn't need to be interrogated very often. I would use I2C if the modules are close together and look at RS232 if there is a long (more than a few metres) connection path to contend with. Jim VK7JH MMedit MMBasic Help |
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| halldave Senior Member Joined: 04/05/2014 Location: AustraliaPosts: 121 |
Jim, Thanks for the suggestion Looks like I need to do further reading and playing. All three Micromite chips will be on the same board. Ill breadboard it with pullups to have a play. One quick question if the RTC is now on the bus, I would now think that all three Micromites will be able to get the RTC? Ill play and see what happens, hopw to get my RTC chips next week regards David |
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| TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6103 |
The micromite's internal clock keeps reasonable time. When I want better, I update it from the RTC every 5 or 10 minutes. The main thing to remember - you can only have one I2C master active at any time. I would leave it with one master and get it to update the slave uMites with the correct time. If you are polling the slaves looking for changes, you may not have much use for the actual time on the slaves anyway. There is nothing worse than different parts of your system running on different times. Jim VK7JH MMedit MMBasic Help |
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Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9309 |
Yes, I agree with Jim. I2C would be a preferable way to do what you are wanting, as this is more-or-less what I2C was designed for, so I understand. Yes, all chips SHOULD be able to access the RTC, if the RTC is on the I2C bus - it's just a matter of addressing the RTC, and reading or writing to it. The normal way with RTC's, is that it will talk back to the master, so not sure if it is possible for a slave I2C device, to read or write to the RTC, but someone else more in the know here would be able to clear that up. Smoke makes things work. When the smoke gets out, it stops! |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9309 |
...a very good point... Smoke makes things work. When the smoke gets out, it stops! |
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| hitsware Guru Joined: 23/11/2012 Location: United StatesPosts: 535 |
> There is nothing worse than different parts > of your system running on different times. Say I wanted 6 pwms and used 2 slaves as above .... Can the clocks of the slaves be synced to the master so that all pwms would be in precise tune ? |
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Geoffg Guru Joined: 06/06/2011 Location: AustraliaPosts: 3196 |
No, you cannot sync them. The internal oscillator used by each Micromite would have a different phase and a slightly different frequency compared to the others. Note that this is difference from the real time clock (time of day) for each chip which can be synchronised reasonably closely. Geoff Geoff Graham - http://geoffg.net |
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| hitsware Guru Joined: 23/11/2012 Location: United StatesPosts: 535 |
There's no pin connected in any way to the oscillators ? But some software adjustment ? > Note that this is difference from > the real time clock (time of day) > for each chip which can be > synchronised reasonably closely. Gotcha ... |
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| Geoffg Guru Joined: 06/06/2011 Location: AustraliaPosts: 3196 |
No, not in the configuration that the Micromite uses. Geoff Geoff Graham - http://geoffg.net |
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