PROM File Formatter Files

This section describes the PROM File Formatter input and output files.

Input Files

You can input one or more BIT files into the PROM File Formatter. A BIT file contains configuration information for a single FPGA device.

Output Files

The PROM File Formatter generates the following files as outputs:

PROM files - The file or files containing the PROM configuration information. Depending on the PROM file format your PROM programmer uses, you can output a TEK, MCS, or EXO file. If you are using a microprocessor to configure your devices, you can output a HEX file.

If the data in the PROM File Formatter is going to be split into multiple PROMs, there will be a PROM file corresponding to each PROM.
PDR file - A PROM description file. The file is an ASCII report file listing all the data streams and BIT files used to construct the PROM file, as well as the load direction and PROM file splitting information. A single PDR file describes all of the data in the PROM File Formatter. The PDR file has the same name as the PROM file and a .pdr extension.

The following is a sample PDR report file for a single data stream written in MCS-86 format. The Devices line indicates the data was split into three serial configuration PROMS.
```
# Created 1998/03/21 11:00:32  
   BeginProm 
     Type   Serial 
     Format MCS-86 
     Info MaxAddress 0x00014642 
     Devices Auto XC17256D XC17256D XC17256D 
     BeginChain 
       StartAddress    0x00000000 
       Info EndAddress 0x00014642 
       Info Size       0x00014643 
       File “/design/fpga1/fpga1.bit”     
     EndChain
   EndProm
```

PRM file - An ASCII file containing a memory map of the output PROM file. If the data in the PROM File Formatter is split into multiple PROM files, there will be a PRM file corresponding to each PROM file.

The following is a sample PRM file.

PROM /design/fpga1/fpga100.prm map: Fri Feb 21 11:00:50 1998 
Format       Mcs86  
   Size         32K 
   PROM start   0000:0000 
   PROM end     0000:7fff 
               Addr1        Addr2 File(s) 
       0000:0000    0000:7fff /design/fpga1/fpga1.bit

Bit Swapping in PROM Files

The PROM File Formatter produces a PROM file in which the bits within a byte are swapped compared to the bits in the input BIT file. Bit swapping (also called “bit mirroring”) reverses the bits within each byte, as shown in the following figure.

Figure 1.3 Bit Swapping

In a bitstream contained in a BIT file, the Least Significant Bit (LSB) is always on the left side of a byte. But when a PROM programmer or a microprocessor reads a data byte, it identifies the LSB on the right side of the byte. In order for the PROM programmer or microprocessor to read the bitstream correctly, the bits in each byte must first be swapped so they are read in the correct order.

In this release of the Xilinx Development System, the bits are swapped for all of the PROM formats: MCS, EXO, and TEK. For a HEX file output, bit swapping is on by default, but it can be turned off by deselecting a Swap Bits option that is available only for HEX file format.

In the XACTstep 6.0 release, all formats were swapped except for the HEX format. If you turn off HEX file bit swapping, you can generate a HEX file that is compatible with a HEX file produced by the XACT 6.0 PROM File Formatter.