**UPGRADE YOUR BROWSER**

We have detected your current browser version is not the latest one. Xilinx.com uses the latest web technologies to bring you the best online experience possible. Please upgrade to a Xilinx.com supported browser:Chrome, Firefox, Internet Explorer 11, Safari. Thank you!

bidirectional

Urgency: Standard

General Description:

When defining a formula for a bus, if you use the value [Z],

the bus is driven to a random state (e.g. 23) instead of

high impedance.

the bus value [Z] in a formula.

One workaround is to break up the formula into sections that

are valid data and sections that are high impedance, then

reassemble the pieces.

NOTE: Only use this workaround if you want the Z value to

propagate through your simulation. If you want to release

the assigned stimulator to allow a tristate buffer to drive

the signal, refer to the other resolution.

Example

-------

You want to put the following pattern onto an 8-bit bus

called DATA: [Z]50 [30]50 [FF]50 [Z]100 [A5]50 [Z]50 [00]50

1. Add the DATA bus to the Waveform Viewer.

2. Select Waveform->Formula->Edit to open the Formula Editor

dialog.

3. Define the following formulas, clicking on Add after

entering each formula:

Z50 <---IMPORTANT: Notice there are no brackets

[30]50[FF]50

Z100

[A5]50

[00]50

4. In the Waveform Viewer, locate the line for the DATA

bus. Click on the DATA line, underneath time 0ns. The

DATA signal name should turn green.

5. Select Waveform->Formula->Insert to open the Formula

Selection dialog.

6. Select the formula you need (Z50 in this case) and click

OK.

7. Now click on the DATA line, right where the first formula

ends.

8. Select Waveform->Formula->Insert and insert the next

piece of the waveform ([30]50[FF]50 in this case).

9. Repeat steps 7 and 8 to construct the entire formula.

If you insert the wrong formula, just select Waveform->

Formula->Replace and select the correct formula. The

incorrect formula will automatically be deleted.

bus, use a Chip Controlled stimulator instead of putting a

'Z' state into your formula.

A stimulator that is in Chip Controlled mode has a weak

driving strength. When applied to the output of a tristate

buffer, the stimulator will be active when the buffer is

disabled, but will be overridden whenever the buffer becomes

enabled.

Example

-------

If you originally wanted to define the following formula:

[Z]50 [30]50 [FF]50 [Z]100 [A5]50 [Z]50 [00]50

Define it like this instead:

[30]100 [FF]50 [A5]150 [00]100

Note that each occurence of [Z] in the original formula has

been absorbed into the next bus value.

After assigning this formula to a bus in the Waveform Viewer,

select the bus and then select Signal->Stimulator Mode->

Chip Controlled.

Was this Answer Record helpful?

AR# 2620 | |
---|---|

Date | 08/12/2003 |

Status | Archive |

Type | General Article |

Page Bookmarked