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LPC4337 JTAG Not working

Question asked by toma daniel on Jan 13, 2017
Latest reply on Jan 16, 2017 by LPCX presso support



on a new designed board with LPC4337 microprocessor we have serious JTAG problems and it seems the impedance on the JTAG pins of the CPUs is not correct (one pin, the SWIO/TMS has an impedance of 50 KOhm, and the others SWDCLK/TCLK, SWO/TDO, NC/TDI is approximately 1.1 MOhms). We had one previous design with LPC4337 CPU which works fine and we had no problem with the JTAG, the impedance on all the pins SWIO/TMS, SWDCLK/TCLK, SWO/TDO, NC/TDI is approximately 1.6 MOhms. We made many boards with both design and in the first lot we had no problem but in the second lot all the CPUs have the same JTAG problem. We use the same company to solder the both boards (both LPC4337 quad flat and BGA) so there should be no problem coming from soldering. The layout is approximately identical, only that the new board design has Ethernet connection and the old board did not had Ethernet. The Ethernet design is exactly the same NGX Xplorer board which works fine! So we are wandering what can cause this JTAG problem on our new design? Can be that in the new board all the CPUs have a fabric problems with the JTAG pins?


best regards


D. Toma