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ixo-usb-jtag - Altera Bus Blaster emulation using Cypress FX2 chip

General information

The code in this directory is for Cypress FX2 (e.g. CY7C68013A) and can be compiled with the SDCC compiler (I tried version 2.6 as shipped with Ubuntu 6.10). Once I had a version that could be compiled with Keil tools (until early 2007), but switched to SDCC because I usually develop on a Linux host.

No logic beside the FX2 itself and only a few external components are required for a basic JTAG adapter. I don't have detailed schematics available; my test setup consists of a FX2 on a custom board where it's directly connected to a Cyclone FPGA.

       |            |
       | Cypress    |
       | CY7C68013A |
       |             |
       | 24 MHz XTAL |

Similar boards are available from - the boards named "Saxo-L" and "Xylo-EM" are pre-wired for use with an adapted version of my code, while "Saxo" and "Xylo" can be used after soldering 4 extra wires:

There's a discussion thread in the fpga4fun forum about this firmware:

Digilent JTAG-USB cable

This cable is supported through the usbjtag-dj_usb.hex firmware. the TDO line is level-shifted through a single transistor, which results in the TDO signal being inverted as it enters the FX2. The firmware takes care of the inversion and returns the correct data.

Note that this only applies to the JTAG-USB cable, and not the JTAG-HS series. The JTAG-HS is based on FTDI chips, not the Cypress FX2.

Digilent Nexys 1 / 2 or Atlys Boards

Through a contribution by Sune Mai, this code can be used with the Digilent Nexys / Nexys2 and Atlys boards.

The hardware-specific code file is hw_nexys.c. Use the usbjtag-nexys.hex firmware file.

Also, you may use the "nexys2prog" script by Andy Ross, available from the same place this code is available from:

Numato Opsis Boards

There is code to support running on the Opsis board from Numato.

The hardware-specific code file is hw_opsis.c. Use the usbjtag-opsis.hex firmware file.

More information about how the FX2 is configured on the Opsis board can be found at

Xilinx JTAG cable

There is code to support running in the "Xilinx Platform Cable USB". A firmware for the XPCU will be built. I've tested this only with unmodified CPLD version 18 (0x12) on a Spartan-3E starter kit, as it was programmed by my WebPack 8.2i. The code needs optimization; yet it is merely a proof of concept.

  • hw_xpcu_i: Access "internal" chain (the XPCU CPLD, IC3, itself)
  • hw_xpcu_x: Access "external" chain (the Spartan 3E, PROM, etc.)

Adapting the code to your hardware

As is, the code assumes the following pin assignment:

  • Port C.0: TDI
  • Port C.1: TDO
  • Port C.2: TCK
  • Port C.3: TMS

Other assignments are possible. If you have your signals connected to bit-addressable I/O pins (port A,B,C or D), I suggest you make a copy of hw_basic.c and adapt the definitions and ProgIO_Init() in it to your needs. The file hw_saxo_l is even simpler to adapt if you want only JTAG and no AS/PS mode. If your signals are not on bit-addressable I/Os (that is, you're using port E), you could base your adaptation on the slower hw_xpcu_i.c.

The USB identification data (vendor/product ID, strings, ...) can be modified in dscr.a51. The firmware emulates the 128 byte EEPROM that usually holds configuration data for the FT245 and which can be read from the host; its content (including checksum) is computed from the data in dscr.a51 as well.

The WAKEUP pin should be high for the re-numeration to work reliably (thanks Jean/fpga4fun!).


Changes since previous release 2008-07-05:

Changes since previous release on 2007-02-15:

  • Jean Nicolle contributed hw_saxo_l.c for the FX2 boards from
  • fx2/Makefile fixed to build correct libfx2.lib even under Windows.

Changes since previous release on 2007-01-28:

  • Initial suppport for running on Xilinx XPCU.
  • New FX2 code, based on USRP2 from the GNU Radio Project;
  • Firmware can now be compiled using SDCC 2.6. No more Keil support.
  • EEPROM content is automatically computed from dscr.a51, including checksum.

Changes since initial release on 2006-04-23:

  • added this readme.txt
  • reorganized my project folder: diff now created from Subversion repository
  • stripped *.dist extension from eeprom.c and dscr.a51
  • added unique proper product and vendor ID (thanks to Antti Lukats!)
  • fixed checksum in eeprom.c
  • added comments about AS/PS mode pins in usbjtag.c
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