Third Party Boards - Software to Development Board Communications

Frozen Content

Communications between Altium Designer and the physical devices on the board is carried out using the technology of the IEEE Boundary Scan Standard 1149.1, more commonly referred to as JTAG.

To successfully 'hook-up' your development board to the Altium Designer software, so that you can program a device on your board with an FPGA design, the JTAG communications must be mapped from a USB (or parallel) port connector on your PC to the actual JTAG pins of the development board. All physical devices have pins pre-assigned for these connections, which will already be pre-routed to the development board's PC interface connector (which we will refer to as the JTAG header). This JTAG chain that is used to program the physical devices is referred to as the Hard Devices JTAG chain.

As well as using JTAG for FPGA device programming, Altium Designer also supports a second JTAG chain, used to communicate to soft devices used in your design inside the FPGA. These soft devices could include a processor core, or virtual instruments included for debugging the FPGA design hardware. This JTAG communications channel is referred to as the Soft Devices JTAG chain. The Nexus 5001 Standard (which builds upon the JTAG communications protocol of IEEE Standard 1149.1) is used as the communications protocol for the soft chain.

To be able to use virtual instruments and processors, the Soft Devices JTAG chain connections must also be made from the Software (via the USB or parallel port connector) to the development board.

In terms of implementing the Soft Devices JTAG chain in the FPGA, you will need access to four free I/O pins on the FPGA itself. These may be available and routed to the development board's JTAG header, if not you should be able to pick up four I/Os on a general purpose I/O header on the board.

Implementing the Soft Devices JTAG chain within your FPGA design is straightforward, see Enabling the Soft Devices JTAG Chain for more information.

As mentioned, the Soft Devices JTAG chain gives access to processor cores and the virtual instruments. Virtual instruments include custom instruments, logic analyzers, digital IO modules, a signal-switching module, a terminal debug console, a frequency counter, and a frequency generator. These instruments are an excellent aid in debugging your design, making it well worth the effort of wiring in the Soft Devices JTAG chain!

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