AVR-Chat

At 08:54 PM 2/4/2004 -0800, harshit suri wrote:
>Hello
>
> From the manual of ATMEGA128 i gather that general
>purpose IO can be used as as SS (Slave Select pin).
>
>I only see one dedicated SS pin = pin 10 (PB0) in the
>data sheet.

The SPI hardware on the 128 can only "see" that pin.
However you can use any other GPIO pin to signal to the other chip(s).


>--How does the SPI module know which are the other SS
>Pins that i have connected as SS to the slaves?

It dosen't.

>--So does this mean that the CPU has to be involved in
>a multi slave situation. as it shall have to pull the
>SS for the slaves low ?

There has to be one SS for each slave.
If you have five slaves, then you'll need to signal each of them, by 
pulling it's SS low, that "I'm talking to YOU".


>--How many slaves can i connect to a single Atmega128?

How big is your circuit board?  How high is up?

>--What is the maximum bit rate of communication
>assuming that i am using a 16Mhz Xtal?

See data sheet, Clock / 4 would be 4 MHz
If you enable the double speed mode, then 8 MHz.

The question really is: How fast can your slaves receive?


>Thankyou
>
>
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