On Wed, 28 Mar 2018 22:38:20 -0500 John Griessen <j...@ecosensory.com> wrote:
> On 03/28/2018 08:16 PM, John Griessen wrote: > > What is the meaning of Vref in the SWD config > > (interface/ftdi/swd-resistor-hack.cfg) > > > > > > " Vref of the adapter should be supplied with a voltage equal > > to the target's (preferrably connect it to Vcc). > > > > # FTDI Target > > # ---- ------ > > # 1 - Vref ----------------- Vcc > > # 3 - nTRST - > > # 4 - GND ----------------- GND > > # 5 - TDI ---/\470 Ohm/\--- SWDIO > > # 7 - TMS - > > # 9 - TCK ----------------- SWCLK > > # 11 - RTCK - > > # 13 - TDO ----------------- SWDIO > > # 15 - nSRST - - - - - - - - - nRESET > > " > > There's VCCIO , type power input, but that's a VCC supply voltage > going into the FTDI JTAG adapter, not an ADC input like I think Vref > should be. VREF is typically used to power the buffers/level translators on the JTAG adapter board that are used to drive the cable. Depending on the design of the JTAG adapter, VREF *may* be unused, but in that case, the JTAG adapter will only support a limited range of target voltages (eg. the chinese ST-Link clones). If the FTDI chip has a VCCIO power pin, that would be exactly what VREF is used for when not using external buffer chips. Having an ADC input that can measure and report back VREF voltage is a nice-to-have feature present on only a few JTAG adapters. cu Mcihael ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ OpenOCD-devel mailing list OpenOCD-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/openocd-devel
