I2C RS485 Chip

Feb 18, 2005 3 Replies
D

A design I was working on was going to use the MAX3140 SPI RS-485 chip. This is an integrated UART and set of drivers. The plan has changed and the RS-485 portion moved to a daughter card. Since all cards will be connected via I2C, I was looking for a similar chip similar to the 3140, but with an I2C interface. Can't find any, but perhaps someone knows of one.



The alternative (and actually a better one in some ways) is to use a processor with I2C port and a UART port, and drivers. Problem with this idea is more software needs to be done (no time) and more board space (not much of that either).



Help appreciated.



Dave,


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You can actually use SPI pins (usually) for I2C. See this page (for example)

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I would also check the datasheet on whatever you are sourcing the SPI from, as it may support I2C directly (with a little register tweaking).

Cheers

PeteS

Dave Boland wrote:

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Tony (remove the "_" to reply by email)

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Tony,

I agree that using a microcontroller has a number of advantages. There are some disadvantages though. One is that is that code will need to be developed and maintained. This translates into development time and cost.

The other problem is that few, if any, microcontrollers can be used as an I2C slave directly. To do this with the PIC, Atmel, Zilog, and most flavors or 8051/52 requires doing it in software with IRQ's. This solution may be a performance problem.

I'm arguing to keep the RS-485 port on the processor card so that SPI can be used (no -CS's are passed to the daughter cards). SPI has a much faster data transfer rate, so it will work much better than I2C (even the high speed I2C).

Dave,

T> The cheapest way will probably be to use a microcontroller that has

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