Honored Contributor
Honored ContributorThanks for the reply,
schematic 1.jpg = entry point (Please note I have added an external switch on /TRST to ensure the TI DSP gets put into a reset state to allow for proper bypassing, i.e. TDO of the TI DSP may not feed through TDI if in a wrong state, confirmed TDI passes through to TDO on scope). schematic 2.jpg = pass through (into and out of TI DSP, includes power rails) schematic 3.jpg = pass through entry into second device (Cyclone II) and exit I realize it is a 14 pin TI interface hooked up to Altera 10 pin. I have an adapter board connecting the required 5 pins from USB Blaster to this interface. I have just noticed that on the TDI into the TI DSP (Schematic 1.jpg) I have forgotten the 1k pull up to 3V3. When I removed the 'yellow flat cable', I actually took my JTAG adapter vero board (very small) and soldered it straight into the USB BLaster (There goes my warranty! :) ) To answer your question, yes we use the XDS510 USB JTAG emulator for communicating with the TI DSP (first in the chain), where the Cyclone II is the second part of this chain, and communication has never been an issue, even when the design is installed in a very noisy environment (i.e. high power motor control cabinet). This leads me to believe that the signal integrity 'on my board' is fine. My next steps are going to be to build up an adapter board with: 1. A buffer stage between the USB Blaster and my design 2. Another path with series termination resistors (100 Ohm) 3. Another path with AC coupled parallel termination resistors I will keep you posted as to the results. It appears to me that many people have signal integrity issues with USB Blaster and multi chain designs. My guess is the USB blaster has very high speed buffers (beyond what it requires) with no adequate transmission line considerations and is very susceptible to over/undershoots. While doing my hack to the USB Blaster this appears to be the case as the design of the USB BLaster was VERY simple on a 2 layer PCB. Cheers, James
