What's Good About Net Groups in Capture? Check Out the 16.5 Release and See!

A NetGroup is a collection of nets. The nets in a NetGroup can be scalar, vector or a combination of both. You can create a NetGroup that consists only of nets (like a bus). You can also create a NetGroup that consists of nets (scalar and/or vector), consists of buses, and consists of other NetGroups. By definition, a NetGroup is a completely heterogeneous collection of nets. The Net group option in the 16.5 release of Allegro Design Entry Capture can be found under Place Netgroups and the shortcut is U:

You can also use the button  to use the option.

Read on for more details…

Types of NetGroup connections in Allegro Design Entry CIS

1. How NetGroups get connected to different bus widths

a) When NetGroup width is more than bus width:
Connect A[0..15] 16 bit NetGroup with B[0..7] 8 bit bus, the whole net will take the name of A[0..15] 16 bit NetGroup. The higher value of the NetGroup always win, hence the NetGroup will be A[0..15]:

 
In the flat net section you can see how the nets get their names. In the flat nets section the Net Name will be A.A0  to A.A15:

 
 

b) Netgroup width is less than the bus width:
Connect A[0..15] 16 bit NetGroup with B[0..31] 32 bit bus; the whole net will take the name of A[0..15] 16 bit NetGroup, but flat nets will contain both bus NetGroup bits and the remaining bus bits (hybrid nets):

 
In the flat net section you can see the NetGroup has nets from A.A0 to A.A15 while remaining bit of the bus B is shown as B16 to B31:

 

c) Netgroup width is same as the bus width:
Connect A[0..15] 16 bit NetGroup with B[0..15] 16 bit bus, the whole net will take the name of A[0..15] NetGroup and the flat nets will be decided by A[0..15] NetGroup:

 

In the flat net section you can see the NetGroup has nets from A.A0 to A.A15:

 


2. How NetGroups gets connected among various NetGroups

a)  When connection is between different NetGroups:
Connect A[0..15] 16 bit NetGroup with B[0..7] 8 bit NetGroup. The combined bus will take the name of A[0..15]. The flat nets will take the name of the NetGroup which has the maximum width. In this case the NetGroup that will be assigned will be A[0..15]:

 


In the flat net section you can see the NetGroup has nets from A.A0 to A.A15:

 
b)  When same width NetGroups are connected:

Connect A[0..15] 16 bit NetGroup with B1[0..15] 16 bit NetGroup, the whole net will take the name of A[0..15] NetGroup and flat nets decided by the priority of NetGroup in lexicographical order (i.e. A[0..15]):

 

The flat nets take the name in lexicographical order or alphabetical order:

As always, I look forward to your comments about this new 16.5 feature.

Jerry "GenPart" Grzenia