Hi I am a bit confused : some evaluation boards use a pull-up (olimex) some other (mcb2103 ) use a pull-down resistor on the RTCK pin. Whats the correct one ? Johan
Jtag RTCK pull-up or pull down ?
Started by ●March 7, 2006
Reply by ●March 7, 20062006-03-07
--- In lpc2000@lpc2..., "Sagaert Johan" <sagaert.j@...> wrote: > I am a bit confused : some evaluation boards use a pull-up (olimex) some > other (mcb2103 ) use a pull-down resistor on the RTCK pin. > > Whats the correct one ? Depends on what you want to do with the board and how your debugger handles RTCK during pulling reset: RTCK is P1.26, which according to UM10120 (this is for Lpc213x) chapter 7.4.3 p.78 determines the usage of P1.26..P1.31: either JTAG pins or GPIO. A pulldown makes these guys debugger pins, while a pullup makes them (initially) GPIOs. Now if your debug cable overrides the pullup while operating the reset, all is well. If it doesn't you have to put a a pulldown otherwise you cannot do JTAG debugging. So a pulldown is a safe bet, while a pullup is advantageous, if you don't want to waste power (internal pullup and external pulldown) in deep sleep mode. Gunter