Re: SPI issues - 3wire vs 4wire

Started by Tom Walsh October 12, 2007
Sam Lee wrote:
> Hi
> I am using a LPC3180 together with an MAC7111 and i want em to communicate
> via SPI. the problem is LPC3180 has a "3 wire SPI", lacking the Chip/Slave
> select, while the MAC7111 has the full 4 wires of SPI including the
> chip/slave select.
> As i want to setup 2 SPI connections with each being the master of one, i
> run into the trouble of the LPC3180 not having a chip select to link
> up with
> the chip/slave select. This is important as i am going to implement it
> with
> DMA and i cannot possibly be toggling an I/O port to function as the
> chip/slave select on the LPC3180.

I think that you just answered your own questions. While I don't know
the LPC3180, on other controllers the solution is to use memory mapped
access to the external device and decoding the ADDR, DMA, RD and WR
signals accordingly. You'll probably need a PLD (gate array) somewhere
on the board to do this.


Tom Walsh - WN3L - Embedded Systems Consultant
"Windows? No thanks, I have work to do..."

An Engineer's Guide to the LPC2100 Series