Can i use two I2C device in 16F877A? - Page 2 - Electronic Circuits Projects Diagrams Free

ESchemainda · 18th June 2008, 08:17 PM

Hello Eric,
yes, I had the same thought. But I rejected it with reference to the slew rate requirements of the I2C signals. But I didn't check it.

Even if my hair ist raising, if it is a serious problem that must be solved, one can use a mini relay to switch. There is no problem with the load or voltage. There are relays which can be controlled directly by the MPU, but one can also use a transistor to drive it. In the net there are a lot of examples available. This solution needs a short delay for debouncing (some ms)between selection of the desired device and the call of the I2C - routine.

I hope, this could be a little help for Hesam.
With regards
Erhard

ericgibbs · 19th June 2008, 07:03 AM

hi Erhard,
The analog selectors can be used with Video signals, at +5V, my data shows switching times in the order of a few tens of nanoSecs.

Which 'slew rate' are you quoting.?? Look at the HEF series.

I know of other users that have connected analog selectors to PIC's/I2C with success.

**Nigel Goodwin** · 19th June 2008, 08:06 AM

Quote:

Originally Posted by ESchemainda

Hello Eric,
yes, I had the same thought. But I rejected it with reference to the slew rate requirements of the I2C signals. But I didn't check it.

Even if my hair ist raising, if it is a serious problem that must be solved, one can use a mini relay to switch. There is no problem with the load or voltage. There are relays which can be controlled directly by the MPU, but one can also use a transistor to drive it. In the net there are a lot of examples available. This solution needs a short delay for debouncing (some ms)between selection of the desired device and the call of the I2C - routine.

First off, why do you feel the need to do this?, do you have clashing I2C addresses?.

If you do, then simply use another pair of pins to create a second I2C bus, but generally if you've got a clash, it's because you've chosen your devices badly.

Pommie · 19th June 2008, 08:53 AM

The OP can put a DS1307 (add 0xD0) and a MCP9800 (add 0x90) on the same bus and have no clashes. Should he want to measure 8 different temperatures then he can use the MCP9801 (add 0b1001NNN0) and put 8 of them on the same bus as the 1307 without a clash. You cannot put two DS1307s on the same bus but why would you want two real time clocks in the same system!

If you wanted to measure 16 temperatures and have two real time clocks on your poor little PIC then you can do as Nigel says and implement a software bus. He even has the routines in his tutorial.

Mike.

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18th June 2008, 08:17 PM	(permalink)
ESchemainda	Can i use two I2C device in 16F877A? Hello Eric, yes, I had the same thought. But I rejected it with reference to the slew rate requirements of the I2C signals. But I didn't check it. Even if my hair ist raising, if it is a serious problem that must be solved, one can use a mini relay to switch. There is no problem with the load or voltage. There are relays which can be controlled directly by the MPU, but one can also use a transistor to drive it. In the net there are a lot of examples available. This solution needs a short delay for debouncing (some ms)between selection of the desired device and the call of the I2C - routine. I hope, this could be a little help for Hesam. With regards Erhard

19th June 2008, 07:03 AM	(permalink)
ericgibbs	hi Erhard, The analog selectors can be used with Video signals, at +5V, my data shows switching times in the order of a few tens of nanoSecs. Which 'slew rate' are you quoting.?? Look at the HEF series. I know of other users that have connected analog selectors to PIC's/I2C with success. __________________ Eric "Good enough is Perfect" PIC tutorials: Gramo's: www.digital-diy.net/ Bill's: www.blueroomelectronics.com/

19th June 2008, 08:53 AM	(permalink)
Pommie	The OP can put a DS1307 (add 0xD0) and a MCP9800 (add 0x90) on the same bus and have no clashes. Should he want to measure 8 different temperatures then he can use the MCP9801 (add 0b1001NNN0) and put 8 of them on the same bus as the 1307 without a clash. You cannot put two DS1307s on the same bus but why would you want two real time clocks in the same system! If you wanted to measure 16 temperatures and have two real time clocks on your poor little PIC then you can do as Nigel says and implement a software bus. He even has the routines in his tutorial. Mike.