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switch between SPI & I2c in software

 
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nader



Joined: 29 Aug 2004
Posts: 12

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switch between SPI & I2c in software
PostPosted: Mon Sep 06, 2004 5:15 am     Reply with quote
i want use spi & i2c in time .i read datasheet & it wrote that only
one of them can be use at the time.
Can i switch between SPI & I2c in software?
is threre any thing wrong with the device that is i2c when i use spi?
ckielstra



Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands

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PostPosted: Mon Sep 06, 2004 5:30 am     Reply with quote
The PIC hardware supports only one of either SPI and I2C. The CCS software however contains a good software I2C driver.
So you can use both: SPI in hardware and at the same time I2C in software (ofcourse not on the same i/o pins).
Ttelmah
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Re: switch between SPI & I2c in software
PostPosted: Mon Sep 06, 2004 10:44 am     Reply with quote
nader wrote:
i want use spi & i2c in time .i read datasheet & it wrote that only
one of them can be use at the time.
Can i switch between SPI & I2c in software?
is threre any thing wrong with the device that is i2c when i use spi?

Technically, there is nothing to stop you switching the hardware in the chip between SPI, and I2C modes, _but_ there are some significant external hardware problems externally. If the chips support a proper 'select' line, so you can ensure only one is listening at a time, then this should be do-able. Otherwise you would have to look through all possible states in each interface, and check these against the data sheets, to see what responses the chips would general. 95% of the possible problems would only lead to data problems, _but_ you have to remember that an I2C slave, can pull the data line low, when extending a transactiion, while on SPI, this line is only ever driven by the master. The potential would then exist for the drivers to be fighting...
Provided you have enough pins, you would be better off, using software I2C, on a seperate pair of pins. This was discussed recently on the forum, and in fine. For instance, I have a 18252, which functions as an SPI slave, using the hardware interface, and controls two other I2C devices using the software interface.

Best Wishes
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