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How best to connect a bus over multiple schematic sheets?

larsen

I draw a bus on sheet1, name it myBus:D[0..15],clk

On another sheet (sheet2) I want to tap into this bus. What is the recommended method to make the bus available there as well?

 

  1. Copying the bus: (by: @sheet1, select_bus, copy_selection, @sheet2, paste) works, but it is awkward.
  2. It works to draw a (new) bus in sheet2 and then copy the entire name string myBus:D[0..15],clk from sheet1 bus name field to sheet2's bus's name string. This is simpler than the first method, but suffers, as the first, from that renaming of bus or bus elements does not work across sheets. You must remember to update all your references manually.

 

Finally, is it correct that cross reference marking (net->xref) is not avilable for busses? I could not figure out to get this to work at least. But xref's  are very practical - check for yourself, a couple of weeks after you drew your schematics.image

 

Thanks for any advice you can offer.

----------------UPDATE:-------------------------------------------------------------------------------------------------------

Methods 1 and 2 seems not to work after all. When I

A) close EagleCad,

B) reload the schematic,

 

there is an error in the .sch file: duplicate name "myBus:D[0..15],clk" at line xyz. And worse still, the schematics will not load any more. Only cure I found was to open the .sch in a text editor and patch the bus name at the indicated location to, lets say "myBusXXXX:D[0..15],clk". Then the schematic loads correctly (and with the name changed on one location). Thanks for using xml database format!

 

Odd that EagleCAd did not complain when the second bus instance was created in the first place.

 

Bottom: Line I thought I understood how to make multi sheet busses. Now I dont any more.

 

Advice is very welcome.

  • 0

    How to connect a bus across sheets?....

     

    Thanks for any hints.

  • 0 in reply to larsen

    On 2/26/2012 6:10 AM, henning larsen wrote:

      How to connect a bus across sheets?....

     

    Thanks for any hints.

     

     

    Hi Henning,

     

    I hope you are doing well. In EAGLE connections are defined by net name,

    so if you want to connect to a bus from a different sheet all you have

    to do is create a net and give the same name as one of the nets assigned

    to a BUS.

     

    Connections are defined by nets, a BUS is like a container for nets so

    you can XREF the nets but not the BUS.

     

    hth,

     

    Jorge Garcia

     

  • 0 in reply to Former Member

    Hello Jorge,

     

    Thank you very much for clarifying this to me.

     

    So I conclude: the bus' name is not used for connections. It can be any name, except, it is only allowed to have one bus with that name in the design. Not even on the same sheet can you have two busses with the same name.

     

    As I do like to group things for clarity I plan to use bus names which hints on their relationship:

    Example:

    On sheet one the databus is called: DataBus1:D[0..15],A[0..19],RW,DS

     

    On sheet two the databus is called: DataBus2:D[0..15],A[0..19],RW,DS

     

    Copy paste from one bus name string to the other should ensure coherence. But dicipline is required when renaming!

     

    I did find one other surprising thing about busses:

    The net you wire to the bus can not be named beforehand unless its name is already a net in the bus. Seems obvious at first, but it means that you have to pass directly from a pin to the bus if you want to benefit from the bus' netname pull-down menu. No intermediate corners - en route on your net is allowed, otherwise you will get the error message that "net N$123 is not member of DataBus2:D[0..15],A[0..19],RW,DS".

     

    For sure, to the experienced user this is not new and maybe if I one day, read the manual I could find this information.

     

    I would like to vote for a better support of multi sheet busses and xref for busses  in future releases.

     

    Thanks again to Jorge for clarifying things.

     

    Regards,

    henning