Re: Xilinx Mode Select Pins

Hi Jon,

"maxascent" <maxascent@xxxxxxxxxxx> wrote in message news:ReidnbnFVd2xakXV4p2dnAA@xxxxxxxxxxxxxxx
Can I just connect the mode select pins (M0-M2) to power/gnd depending on
my required programming mode or do I need to connect them to resistors? If
I select a master serial mode will it prevent me from using JTAG.

Sorry, I can't tell which family you are using. However, here's a snippet from page 47 in UG332: Spartan-3 Generation Configuration User Guide.
http://www.xilinx.com/support/documentation/user_guides/ug332.pdf

"?During configuration, the M[2:0] pin may be tied directly to power or ground, tied High or Low using external resistors, or actively driven by an external component."

In many designs, I like to use pull-up/pull-down resistors as it always gives me the option to overdrive the resistor values and change the configuration mode. However, if you never need that flexibility, then the resistors are just extra space and expense.

IIRC, JTAG is always functional, even if using Master Serial configuration mode. However, depending on the family on the programmed/unprogrammed status of the serial PROM, you can run into some issues. You can still reprogram the serial PROM via JTAG. You can still run ChipScope. However, the follow Answer Record seems to indicate that there might be problems if you are attempting to directly program the FPGA if the PROM is already programmed. For some reason, I thought that this was fixed in recent released, but perhaps not.
http://www.xilinx.com/support/answers/9013.htm

Again, some of the nuances depend on the specific FPGA family.
===============================================
Steven K. Knapp
Prevailing Technology, Inc.
Web: www.prevailing-technology.com



.

Relevant Pages

  • Re: How inaccurate is a 555 or 7555 REALLY?
    ... John Fields wrote: ... ISTR that 1/8 watt resistors and 1N914s were available back then, ... series - with in-system programming, ... the logic into a single modern PLD. ...
    (sci.electronics.design)
  • Re: How inaccurate is a 555 or 7555 REALLY?
    ... John Fields wrote: ... ISTR that 1/8 watt resistors and 1N914s were available back then, ... series - with in-system programming, ... There is a certain learning curve in learning how to use Boolean logic, ...
    (sci.electronics.design)
  • Re: Mixed voltage in JTAG chain.
    ... If you are looking at something like a Spartan-3 at 2.5V with say Platform ... Flash devices then you really want to put series resistors in line to the ... Just be careful that your programming cable is happy with ... as we have found testing competitor cables with some of our products. ...
    (comp.arch.fpga)
  • Re: How inaccurate is a 555 or 7555 REALLY?
    ... John Fields wrote: ... ISTR that 1/8 watt resistors and 1N914s were available back then, ... series - with in-system programming, ... There is a certain learning curve in learning how to use Boolean logic, ...
    (sci.electronics.design)
  • Re: coutdown 555 timer values?
    ... > The other proposal, using a microcontroller, does require the ... > Now on to programming languages. ... > and give some insight into wiring 555 circuits. ... directly to the uP, through a three wire cable (OK, plus 2 resistors). ...
    (sci.electronics.basics)
Loading