I2C or SPI?

matt redmond · Joined: 26 Sep 2003 Posts: 6

Hi,

Need to interface a EEPROM, probably a MicroChip part, with an '877A. Any thoughts on whether I should go with I2C or SPI? Any advantages to using one over the other?

The only thing I see is that with I2C I can have multiple devices on the bus, where SPI looks to be single-ended. I want whatever is easy and works reliably with the functions provided by CCS' C.

-matt redmond

Snoopy · Guest

Hi

SPI is very easy to use instead of I2C.
you can put a lot of device on SDI, SCK SDO,
one pin for each CS. you can use demux (for CS PIN)
if you are using some SPI device. I have never use I2C
a can not take it about the speed.

I use SPI communication a 6Mhz, 24Mhz crystal / 4= 6Mhz SPI communiation.

matt redmond · Joined: 26 Sep 2003 Posts: 6

So SPI is a multi-device interface?

You are saying I can put multiple devices sharing the SDI, SCK and SDO pins and then I need one pin for each device to use for CS. Right?

Under what circumstances would I use a demux for CS? When I have more than 2 devices?

Kieran · Joined: 28 Nov 2003 Posts: 39 Location: Essex UK

I use SPI a lot, it is multi-device but you do need 1 PIC pin to drive each Chip select as Snoopy says. I have connected EEPROMs, display drivers, I/O expand, Maxim UART etc. etc. I have used I2C with EEPROMs but I think it is more difficult to use however fewer pins required to drive it.

snoopy · Guest

Personnally,if i have some device and i can't put in in daisy chain.
i am using a demutiplexer for CS, that is permit to reduce pin from
uChip. but if you have some free pin chose one pin for each SPI.

like i am using a MAX7221, an you can put it in daisy chain mode.
i have only one cs pin for all max7221