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======  Xilinx Virtual JTAG Cable with USB FTDI chip FT220X ======


[[http://www.mlab.cz/Modules/CPLD_FPGA/XILINX_XVC/XVC_FT220X02A/DOC/XVC_FT220X02A.cs.pdf|Original document XVC_FT220X02A]]

This is set of software and electronic hardware created by [[cs:credits|MIHO]]. It is intended to obtain better accessible method of programming Xilinx FPGAs. More documents describing this method are available on 
[[http://www.mlab.cz/Server/GenIndex/GenIndex.php?path=%2FModules%2FCPLD_FPGA%2FXILINX_XVC&lang=cs|MLAB documents list page]].


===== Description of solution =====

To work with Xilinx FPGA hardware programmer is needed. It allows load of schema binary in to the chip. This method can be realized  by connecting the FPGA chip to the JTAG interface device.

XILINX ISE development suite for FPGAs supports XVC protocol. This protocol allow remote TCP/IP connection to the JTAG device which is connected to the FPGA chip at the remote end. 

==== Working principle ====

This module creates the virtual JTAG cable to the FPGA. This is based on FTDI FT220X USB interface chip and JTAG connector on its pins. Communication itself is realized over TCP/IP network thus of this FPGA can be located outside of developer working place. The whole process is illustrated on following picture:

{{ :cs:fpga:schemacyklu_small.png?direct&500 |}}

==== Electronic construction ====

The module contains minimum number of parts because majority of functionality components is resolved by control software. The most important for user are some connectors and indicating LEDs with following meaning:

^ LED ^ Color ^ Function ^
|TGT D1 | Red | Indicate voltage on JTAG programming connector |
|ACT D2 | Green | Data transmission activity |
|USB D3 | Red | Indicates USB power voltage |

There are two jumpers on the board of module: Jumper J3 marked as VIO PWR - this jumper selects JTAG working voltage (Internal 3.3 V regulated by FTDI chip or TGT voltage from JTAG connector).

Jumper 4 provides +5V power to target device from USB. 


==== Use of XVC module ====

For use of this module XILINX development suite with iMPACT software is needed. In addition you need mlab_xvcd service utility. 

=== Service software ===

The XVC module is controlled by OpenSource software [[cs:xvc_software|mlab_xvcd]]. This utility is fully supported in windows operating system Linux version is in development stage.

=== Use of XILINX ChipScope ===

ChipScope is valuable tool enabling the monitoring of internal octions in FPGA by integrated logical analyzer. It can be used in combination with XVC system. 

==== System limitation ====

This XVC system currently are not able to write to FPGA internal FLASH memory (due to software limitations). Then schema binary must be loaded after every power up cycle or [[cs:jtagft2232v|JTAGFT2232V02A]] programmer must be used.