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viscomjim
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Joined: 08/01/2014
Location: United States
Posts: 925

Posted: 06:00am 12 Jun 2015

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I am working on a project that consists of the following...

2 identical boards, a uMite with a I2C eprom (24lc32A). The clock and data line will be pulled high using 4.7k resistors as I would like to use 400khz comms. There will arise a situation where the eeprom data from one board will need to be transferred to the eeprom of the other board. This is all surface mount so swapping eeproms in sockets won't work.

So what I was thinking is this... there will be two buttons on each board. If you push one button while powering up the board, it will run a program to become a "master". On the other board you push the other button during power up and that will make it a slave. The slave board will have a jumper to change the eeproms address by one. By slave in this sense, I mean the uMite is just idle. The master will then address the slaves eeprom (different address) and copy data from the master eeprom to the slave eeprom. Both boards are connected using 3 dupont wires for clock, data and ground.

Once the transfer is complete, the units are powered down, the jumper is replaced, clk, data and gnd wires removed, powered back up with no buttons pushed and both boards carry on with their normal operation.

My main concern is both boards have eeproms on the I2C bus and therefore have 4.7k pull ups on the clk and data lines. When these two boards are connected, will the "parallel" resistors pose any kind of problems. Do I need to worry about the speed if the wires are short (6")?Edited by viscomjim 2015-06-13

bigmik

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Joined: 20/06/2011
Location: Australia
Posts: 2870

Posted: 12:14am 13 Jun 2015

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ViscomJim,

4k7 is usually for 200kHz and 2k for 400kHz (10k for 100kHz) so two 4k7 in parallel with be close enough to 2k ... If they work at 400kHz with 4k7 pullups by themselves then you shouldnt have any problems with them in parallel.

Regards,

Mick

Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<<

viscomjim
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Joined: 08/01/2014
Location: United States
Posts: 925

Posted: 12:37am 13 Jun 2015

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Thanks Mick, I'm going to breadboard this out before of course, I was just curious if anyone ran into this in the past. I was not aware of the 2k for 400khz, so that is a good thing.

bigmik

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Joined: 20/06/2011
Location: Australia
Posts: 2870

Posted: 12:56am 13 Jun 2015

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No Problem Jim,

From Geoff's MicroMite Manual

Both of these pins should have external pullup resistors installed (typical values are 10KΩ for 100KHz or 2KΩ
for 400 kHz).

Regards,

Mick

Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<<

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