Hi 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. Cheers Jon
Xilinx Mode Select Pins
Started by ●September 23, 2008
Reply by ●September 23, 20082008-09-23
On Sep 23, 7:03 am, "maxascent" <maxasc...@yahoo.co.uk> wrote:> Hi > > 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. > > Cheers > > JonWhere is Peter now that we really need him? ;) IIRC, these pins have internal pullups, so all you need to do is ground the '0' pins. If pulling up, I would use a current limiting resistor. There may be a situation where the board Vcc doesn't match the internal Vcc of the configuration section. What does the data sheet recommend? And you can still enter JTAG mode with the mode pins set for serial programming. At least on some chips; which chip did you say you were using?
Reply by ●September 23, 20082008-09-23
Hi> IIRC, these pins have internal pullups, so all you need to do is > ground the '0' pins.Yes, you could ground them. I use a board where this pin's are directly grounded. cheers ben
Reply by ●September 23, 20082008-09-23
Some xilinx fpgas, with mode pins set to a non-jtag mode, cannot enter jtag configuration mode (via jtag command) until/unless they are successful in configuring via the mode pin designated method. In other words, if you tie the mode pins to designate configuration from a serial prom, and you don't have a valid configuration in your prom, you cannot use jtag to command the fpga to configure via jtag. Andy
Reply by ●September 23, 20082008-09-23
Hi Jon, "maxascent" <maxascent@yahoo.co.uk> wrote in message news:ReidnbnFVd2xakXV4p2dnAA@giganews.com...> 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
Reply by ●September 24, 20082008-09-24
Hi All Thanks for the help. I am using a Spartan 3E. Must of missed that bit in the user guide. I am planning to use an external SPI flash memory to store the config so if I just connect the pins directly to power/gnd I think I should still be ok for using JTAG once in a while. Jon
Reply by ●September 24, 20082008-09-24
On Sep 23, 5:54=A0pm, "Steve Knapp" <steveD.O.TknappA.Tprevailing- technologyD.O.Tcom> wrote:> IIRC, JTAG is always functional, even if using Master Serial configuratio=n> mode. =A0Normal JTAG functions are always available. JTAG configuration functions (on some devices, including at least V2) are not available unless the mode pins are set to JTAG, or a valid configuration has already been completed. Don't ask me how I know... ;^) Andy
Reply by ●September 24, 20082008-09-24
On Sep 24, 5:45=A0am, Andy <jonesa...@comcast.net> wrote:> On Sep 23, 5:54=A0pm, "Steve Knapp" <steveD.O.TknappA.Tprevailing- > > technologyD.O.Tcom> wrote: > > IIRC, JTAG is always functional, even if using Master Serial configurat=ion> > mode. =A0 > > Normal JTAG functions are always available. JTAG configuration > functions (on some devices, including at least V2) are not available > unless the mode pins are set to JTAG, or a valid configuration has > already been completed. Don't ask me how I know... ;^)Yeow! Does anyone know if this is true for V5? I've got a board going to layout with the mode pins grounded for master serial, but I want to be able to do JTAG as well just in case. This is on a BGA part, so if I need to tweak these pins, I'll have to route them out or be screwed. Eric
Reply by ●September 24, 20082008-09-24
Hi> Yeow! Does anyone know if this is true for V5? I've got a board going > to layout with the mode pins grounded for master serial, but I want to > be able to do JTAG as well just in case. This is on a BGA part, so if > I need to tweak these pins, I'll have to route them out or be screwed.It worked for me! cheers ben
Reply by ●September 25, 20082008-09-25
On Sep 24, 10:22=A0am, emeb <ebromba...@gmail.com> wrote:> On Sep 24, 5:45=A0am, Andy <jonesa...@comcast.net> wrote: > > > On Sep 23, 5:54=A0pm, "Steve Knapp" <steveD.O.TknappA.Tprevailing- > > > technologyD.O.Tcom> wrote: > > > IIRC, JTAG is always functional, even if using Master Serial configur=ation> > > mode. =A0 > > > Normal JTAG functions are always available. JTAG configuration > > functions (on some devices, including at least V2) are not available > > unless the mode pins are set to JTAG, or a valid configuration has > > already been completed. Don't ask me how I know... ;^) > > Yeow! Does anyone know if this is true for V5? I've got a board going > to layout with the mode pins grounded for master serial, but I want to > be able to do JTAG as well just in case. This is on a BGA part, so if > I need to tweak these pins, I'll have to route them out or be screwed. > > EricJTAG certainly works for ChipScope with mode pins grounded. I am doing that right now.
