Re: SPI problem

On Tue, 13 Jan 2004, David VanHorn wrote:

>
> What am I missing here?
>
> I'm setting up SPI as a master on a mega 8, but it never outputs any
> data, and SPIF never sets.
>
> SPSR is 0x01 ( I want double speed mode)
> SPCR is 0x50 ( I want fast, master, enabled, no int)
>
> DDRB is 0xEF
> PORTB is 0x14

Does setting PORTB to 0x24 help? I see this in the datasheet:

  PB2 -> SS*
  PB3 -> MOSI
  PB4 -> MISO
  PB5 -> SCK

Also, you might want to set PB2 high. The sim might be confusing things
and think the DDRB:2 being high is not sufficient to stop the SS* signal
from putting the part into slave mode.

Might also consider clearing DDRB4 in DDRB since it's an input.

I assume you tried simple SPI output in a real device already and it
works. I've had best results if I make sure that the SPI bits of DDRB
and PORTB are the same.

> PINB is 0x0C, but I don't think it matters.
>
> When I drop the data in SPDR (in sim) the data dissapears on the next
> cycle, but that's it. Nothing happens on the PORTB pins, and SPIF in
> SPSR never sets, so I hang waiting for transmit to complete.

If it works in the real device, but not in the sim, I would suspect a
bug in the sim. Which sim are you using?

Ted Roth