> i can predict problems when placing ground directly at the RS pin at mcp2551?
If you read the Data Sheet it states that "High-Speed mode is selected by connecting the RS pin to VSS." So connecting it to ground is a valid mode if you want to disable the slew rate limiting.
> the reason i am asking is that i would like to save the
> need for a 4.7kohm resistor and i would like to enable
> standby mode by connecting the pin the microcontroler
> (i can still do that with two pins but i would rather
> use one and no resistor)
Two pins? From what I'm reading you shouldn't connect the pin through a resistor to ground AND drive it from a CPU as the CPU will then be driving current into that resistor when it drives the pin high. That would be wasting current when you are trying to be in a low power mode. You should connect the resistor from the MCP2551 to the CPU pin. Drive high for shutdown and drive low to enable (and set the slew rate).
> if removing the resistor is not advised would it
> be a problem using 10khm resistor instead of 4.7khm?
Why not read the Data Sheet? Figure 1-1 (SLEW RATE VS. SLOPE-CONTROL RESISTANCE VALUE) shows how the slew rate changes with different resistor values. I don't know where you get 4k7 from as the minimum value shown there is 10k. The maximum current given in the DC Characteristics Table is 200uA and at 2.5 (Vdd/2) that corresponds to a minimum resistor value of 12k5.
post edited by tom_usenet - 2012/03/15 15:27:02