At 21:48 08-11-07 +0100, you wrote: >Grant Edwards schrieb: >> Can anybody confirm that the JTAG applications work when there >> are other devices besides the MSP430 in the TJAG chain? > >i can't. ;-) > >as i understand, even disabled devices in the change add one cycle delay >when shifting data through the registers of the JTAG. so the JTAG code >talking to the MSP430 would need to know that additional delay when reading.
This is strange. The JTAG specification is very clear on this point. An unused device should be loaded with a pass-through command which sets the 'delay' to 1 bit. But there is a problem though... JTAG is often implemented in a rather stupid way which changes the data and the clock at the same time. If the clock is loaded heavely by a longer string of devices, the clock will start to run late causing the chain to fail because the setup time isn't met any more. Adding an RC delay to the TDI and TMS sometimes solves these sort of problems. Nico Coesel
