PIC connected to a PC through SMbus

Patrik Berglund · Guest

Hi!

Some circuits on a modern PC-motherboard communicates through SMbus. To keep it simple, I wan't to connect my 16F877 to this bus and read data from a winbond chip. I have read the 16F877 datasheet, but I didn't get much wiser.

I´m using PCW 2.660

Any good ideas?
___________________________
This message was ported from CCS's old forum
Original Post ID: 12572

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

:=Hi!
:=
:=Some circuits on a modern PC-motherboard communicates through SMbus. To keep it simple, I wan't to connect my 16F877 to this bus and read data from a winbond chip. I have read the 16F877 datasheet, but I didn't get much wiser.
:=
:=I´m using PCW 2.660
-----------------------------------------------------------

I haven't used a SMBus device, but it's very similar to i2c.
Here's an appnote which compares the two:
<a href="http://www.maxim-ic.com/appnotes.cfm/appnote_number/356/ln/en" TARGET="_blank">http://www.maxim-ic.com/appnotes.cfm/appnote_number/356/ln/en</a>

I suggest that you enable the SMBus levels, by setting the
CKE bit. Then use PIN_C4 for SDA and PIN_C3 for SCL.
Then use the built-in software i2c functions of the compiler.
(Your version of the compiler does not support hardware i2c).

Example:

<PRE>
#include <16F877.h>
#fuses HS, NOWDT, NOPROTECT,PUT,BROWNOUT, NOLVP
#use Delay(clock=8000000)
#use i2c(Master, SDA=PIN_C4, SCL=PIN_C3)
 
#bit CKE_BIT = 0x94.6
 
main()
{
CKE_BIT = 1; // Enable SMBus levels
 
// Access your i2c device with the CCS i2c functions.
i2c_write(0xA0);
i2c_write(addr);
// etc.
 
 
while(1);
}
</PRE>
___________________________
This message was ported from CCS's old forum
Original Post ID: 12579

Patrik Berglund · Guest

:=:=Hi!
:=:=
:=:=Some circuits on a modern PC-motherboard communicates through SMbus. To keep it simple, I wan't to connect my 16F877 to this bus and read data from a winbond chip. I have read the 16F877 datasheet, but I didn't get much wiser.
:=:=
:=:=I´m using PCW 2.660
:=-----------------------------------------------------------
:=
:=I haven't used a SMBus device, but it's very similar to i2c.
:=Here's an appnote which compares the two:
:= <a href="http://www.maxim-ic.com/appnotes.cfm/appnote_number/356/ln/en" TARGET="_blank"> <a href="http://www.maxim-ic.com/appnotes.cfm/appnote_number/356/ln/en" TARGET="_blank">http://www.maxim-ic.com/appnotes.cfm/appnote_number/356/ln/en</a></a>
:=
:=I suggest that you enable the SMBus levels, by setting the
:=CKE bit. Then use PIN_C4 for SDA and PIN_C3 for SCL.
:=Then use the built-in software i2c functions of the compiler.
:=(Your version of the compiler does not support hardware i2c).
:=
:=Example:
:=
:=<PRE>
:=#include <16F877.h>
:=#fuses HS, NOWDT, NOPROTECT,PUT,BROWNOUT, NOLVP
:=#use Delay(clock=8000000)
:=#use i2c(Master, SDA=PIN_C4, SCL=PIN_C3)
:= 
:=#bit CKE_BIT = 0x94.6
:= 
:=main()
:={
:=CKE_BIT = 1; // Enable SMBus levels
:= 
:=// Access your i2c device with the CCS i2c functions.
:=i2c_write(0xA0);
:=i2c_write(addr);
:=// etc.
:= 
:= 
:=while(1);
:=}
:=</PRE>

Thanks :)

Now i just got to figure out what adress the winbond chip uses. Btw, the SMbus is probably used by som integrated chips on the motherboard. Is there somthing I should think about before connecting the pic to the SMbus ?
___________________________
This message was ported from CCS's old forum
Original Post ID: 12616

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

:=:=:=Hi!
:=:=:=
:=:=:=Some circuits on a modern PC-motherboard communicates through SMbus. To keep it simple, I wan't to connect my 16F877 to this bus and read data from a winbond chip. I have read the 16F877 datasheet, but I didn't get much wiser.
:=:=:=
:=:=:=I´m using PCW 2.660
:=:=-----------------------------------------------------------
:=:=
:=
:=Now i just got to figure out what adress the winbond chip uses. Btw, the SMbus is probably used by som integrated chips on the motherboard. Is there somthing I should think about before connecting the pic to the SMbus ?
-------------------------------------------------------------

If you connect your PIC to an existing SMbus on the
PC motherboard, there could be a problem. That bus will
already have a "bus master" on it. It will likely have one
master, and several slave devices. If you try to put another
master (your PIC) on the bus, there could be bus "collisions".
(The motherboard master, and your PIC could try to use the
bus at the same time). The motherboard might not work with a
2nd master on the bus.
___________________________
This message was ported from CCS's old forum
Original Post ID: 12632

Patrik Berglund · Guest

:=:=:=:=Hi!
:=:=:=:=
:=:=:=:=Some circuits on a modern PC-motherboard communicates through SMbus. To keep it simple, I wan't to connect my 16F877 to this bus and read data from a winbond chip. I have read the 16F877 datasheet, but I didn't get much wiser.
:=:=:=:=
:=:=:=:=I´m using PCW 2.660
:=:=:=-----------------------------------------------------------
:=:=:=
:=:=
:=:=Now i just got to figure out what adress the winbond chip uses. Btw, the SMbus is probably used by som integrated chips on the motherboard. Is there somthing I should think about before connecting the pic to the SMbus ?
:=-------------------------------------------------------------
:=
:=If you connect your PIC to an existing SMbus on the
:=PC motherboard, there could be a problem. That bus will
:=already have a "bus master" on it. It will likely have one
:=master, and several slave devices. If you try to put another
:=master (your PIC) on the bus, there could be bus "collisions".
:=(The motherboard master, and your PIC could try to use the
:=bus at the same time). The motherboard might not work with a
:=2nd master on the bus.

I thought the SMbus used arbitration ?
___________________________
This message was ported from CCS's old forum
Original Post ID: 12635

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

:=:=:=:=:=Hi!
:=:=:=:=:=
:=:=:=:=:=Some circuits on a modern PC-motherboard communicates through SMbus. To keep it simple, I wan't to connect my 16F877 to this bus and read data from a winbond chip. I have read the 16F877 datasheet, but I didn't get much wiser.
:=:=:=:=:=
:=:=:=:=:=I´m using PCW 2.660
:=:=:=:=-----------------------------------------------------------
:=:=:=:=
:=:=:=
:=:=:=Now i just got to figure out what adress the winbond chip uses. Btw, the SMbus is probably used by som integrated chips on the motherboard. Is there somthing I should think about before connecting the pic to the SMbus ?
:=:=-------------------------------------------------------------
:=:=
:=:=If you connect your PIC to an existing SMbus on the
:=:=PC motherboard, there could be a problem. That bus will
:=:=already have a "bus master" on it. It will likely have one
:=:=master, and several slave devices. If you try to put another
:=:=master (your PIC) on the bus, there could be bus "collisions".
:=:=(The motherboard master, and your PIC could try to use the
:=:=bus at the same time). The motherboard might not work with a
:=:=2nd master on the bus.
:=
:=
:=I thought the SMbus used arbitration ?
---------------------------------

The spec does say it uses arbitration. I haven't used
the bus before, so I just gave you some of my concerns I had,
without reading the spec.
<a href="http://www.smbus.org/specs/smbus110.pdf" TARGET="_blank">http://www.smbus.org/specs/smbus110.pdf</a>
___________________________
This message was ported from CCS's old forum
Original Post ID: 12636