At 23:12 08-11-07 +0100, you wrote: >N. Coesel schrieb: >> 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. > >that's what i meant. the MSP430 also does this on command or fuse check >failure. > >but doesn't that say that you need one additional clock when reading a >register? compared to the msp430 alone without the other device in pass >through. so for example reading the msp430 JTAG identification will be >one bit position off when reading 8 bits as usual.
Actually, you'll need to compensate for the number of devices in that chain to position the data correctly. It has been a while since I wrote a jtag implementation, but the first thing my routine did was probing the number of devices in the chain in order to determine the amount of padding bits required to get the right data in and out of a device. Nico Coesel /---------------------------------------------------------------\ | N C T Developments | |Innovative solutions for: | | Electronics * Computers * Internet * Networking * Telecom | \---------------------------------------------------------------/
