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Visitor jzmuda
Visitor
21,531 Views
Registered: ‎01-11-2010

How to use "bus tap" in schematic capture in ISE 10.1

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Hi!  I am a beginning ISE user.  I have so far run a couple of projects successfully.  (E.G., a simple 4-bit Johnson counter.)

 

I am in the process of modifying the Johnson counter example to include a number of counters, concatenated to slow down the clock.

 

Specifically, I have two counters what I am chaining together to get a greater count.  The first is a 16-bit counter and the second is an 8-bit counter.  I am connecting the top bit of the first (16 bit) counter to the clock input of the second 8 bit counter.  So I am trying to connect "Q[15]" on the first counter to "clk" on the second.

 

But I am having a hard time figuring out how to use the "bus tap" tool to accomplish this.

 

I tried using it both as a "wire" and as a "net".  (The two varieties described in the help pages.)

 

But, I seem to be unable to properly name the single bit of the bus that I want to tap. 

 

Anyone have a hint as to how to do this?

 

I see the "options" dialog, where I can select the "use bus tap" check box.  And then the tow name fields - only one of which it seems I can actually enter a name into.  And when I try to enter Q[15] it doesn't seem to like it.  When I generate it still complains about the signals that I am connecting being of different sizes.

 

Thanks in advance for any help or clues you can give me.

 

Jim

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Advisor eilert
Advisor
26,422 Views
Registered: ‎08-14-2007

Re: How to use "bus tap" in schematic capture in ISE 10.1

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Hi Jim,

using busses in ISE schematic capture follows a quite strict procedure:

 

1) draw a wire for the bus (if it's connected to a bus input or output it's widened automatically.

2) Name the Bus (e.g. Counter(12:0) )

3) In order to add bus taps, first activate the "Automatically add bus taps" Option 

4) draw your wires from the component pin to the bus. (The tap should appear now, sometimes it fails, then delete and rewire)

5) After drawing all the bus tapped wires use add net name to name the lines. e.g. Counter(0)   to   Counter(12)

    See the Option field. There are powerful tools to simplify this task.

 

Have a nice synthesis

  Eilert

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Adventurer
Adventurer
21,519 Views
Registered: ‎03-27-2008

Re: How to use "bus tap" in schematic capture in ISE 10.1

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You should be able to name your output net as Q(15:0), then for your clk signal, name the input net as Q(15).

Note the bracket type. I do this all the time and never use bus taps.

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Advisor eilert
Advisor
26,423 Views
Registered: ‎08-14-2007

Re: How to use "bus tap" in schematic capture in ISE 10.1

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Hi Jim,

using busses in ISE schematic capture follows a quite strict procedure:

 

1) draw a wire for the bus (if it's connected to a bus input or output it's widened automatically.

2) Name the Bus (e.g. Counter(12:0) )

3) In order to add bus taps, first activate the "Automatically add bus taps" Option 

4) draw your wires from the component pin to the bus. (The tap should appear now, sometimes it fails, then delete and rewire)

5) After drawing all the bus tapped wires use add net name to name the lines. e.g. Counter(0)   to   Counter(12)

    See the Option field. There are powerful tools to simplify this task.

 

Have a nice synthesis

  Eilert

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Visitor jzmuda
Visitor
21,466 Views
Registered: ‎01-11-2010

Re: How to use "bus tap" in schematic capture in ISE 10.1

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Thanks btrac.  Thanks  Eilert.

 

I was finally able to get my "bus tap" in place. Following Eilert's instructions.

 

The key point (not mentioned by Eilert - probably because it was too obvious) was that the "add Bus Tap" action doesn't actually add the "bus tap". Instead it sets the properties of the "bus tap" you are about to add.  (Specifically, this is where you set the bus name and "tapped" signal name. E.G., Counter(7:0) and Counter(7).)   

 

You actually add the bus tap (by selectiing "Automatically ad bus tap") when you draw a wire from a component pin (in this case the next counters clock input) to the named bus.

 

Oh, and one more item to note.  I had to make sure to name the component side of this "wire" ("bus"?)  (using the rename bus conmand) to some name that idenitifed the actual signal being tapped.  (Something like Counter(7)).   

 

Since I was concatenating two counters, I had to create two taps.  So, even after I got the first one right, I couldn't really remember how I had done it.  It wasn't until after I did the second one that I really got the procedure down.

 

Let's see if I can remember how to do this the next time.

 

Thanks, again, to both of you.

 

Jim

 

P.S. btrac, I wish I knew how to select a component and then edit the net name that each component pin is connected to.  I don't know how to do that.  The only way I know how to connect anything is by drawing wires. Using the add wire tool.  When I select a component, and try to edit its properties NONE of the properties seem to be of any interest to me.  Nothing about pins is mentioned.    I would like to know how to edit the net connections of the pins on a component is some dialog box called up when I double click on a component.  And then ISE would re-draw the schematic, showing the new connections I just made, textually.  Or something like that.  Is that something like what you were referring to? Can the ISE 10.1 schematic editor work that way?

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Visitor rbwilliams
Visitor
21,303 Views
Registered: ‎02-11-2010

Re: How to use "bus tap" in schematic capture in ISE 10.1

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Hi,

New to the forum

I am a complete neb to CPLD and the ISE myself. I would love to learn how you created your johnson counters! I was thinking of modeling the CD4017, but I have no idea how to do it.

 

Thanks,

Roger

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Visitor jzmuda
Visitor
21,295 Views
Registered: ‎01-11-2010

Re: How to use "bus tap" in schematic capture in ISE 10.1

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see the examples directory under the ise tool, rbwilliams,Hi
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