AR# 367: XACT 5: Acessing fast input pins for High Density Function Blocks
XACT 5: Acessing fast input pins for High Density Function Blocks
The XACT 5 software for the XC7300 family does not directly support fast input (FI) pins for High Density Function Blocks.
How can these fast inputpins be accessed?
NOTE: The fast input paths to High Density Function Blocks are being obsoleted from the silicon. The following workaround is valid for the version 5.x software only.
Here is the workaround that enables the use of fast inputs for HDFBs on the 7300 family and function blocks on the 7236. There are still only 21 inputs to the AND array.
1. Write equations, or design a schematic, as if the inputs were not fast inputs.
2. Pin assign the fast input pins. Also pin assign the outputs which use these inputs so they end up in the correct function blocks.
3. Make a <design>.FI file in the design directory. List all fast input pins in this file. Use pin numbers such as PIN23, PINB12, etc. Do not use design signal names. The format is a list of pad names, separated by new-lines, carriage returns, spaces and tabs. Only words starting with 'PIN' are read. Other words are ignored.
4. Integrate as normal with commands FITEQN or FITNET.
5. Make a programming file with MAKEPRG. The <design>.FI file is read and the fast input paths are enabled at this point.
6. Error messages are output to the screen and to the <design>.PRG file. The PRG file will not contain programming data if there are errors; just the error messages willl appear in the file.
The software makes the following checks:
- Verify that the pin is a pin with fast input capability. - Verify that the input has a direct connection, without UIM-ANDing, to logic placed in the correct function block. It is valid for the input to also use the UIM path to other function blocks.
If the fast inputs are enabled successfully, there is a message for each fast input in the programmer log file <design>.LGP.