Lpc2000

--- In lpc2000@yahoogroups.com, <sig5534@h...> wrote:
>
> > > You can't get anywhere near that on ARM7TDMI-S parts which we 
are 
> > > dicussing,
>  
> Correct.  The maximum speed I can use with the JTAGjet is 4MHz on 
these LPC parts.
> BTW, I was incorrect before, the JTAGjet goes to 30MHz when I 
checked it again.

There has been no information provivded or pointed to that puts the 
limiting factor on the ARM7TDMI-S part itself. 

Adaptive RTCK use overcomes the 1/6 rule when the core is not in a 
debug state. In a debug state there is no clock relevant to JTAG to 
synchronise to.  Yes I am aware of the 'switch to system speed and 
back to debug' issue.

There are lots of reasons why speed becomes maxed out. Not the least 
of which is wiring. 

It would be nice to know what the limiting factor is to investigate 
if it can be overcome and so use the more capable debug tools to 
their full capacity. 

John Heenan

> >> Try this link.  http://www.arm.com/support/faqip/3732.html.  
Extracting
> >> the relevent details, "If the RTCK output is not used, it is 
required
> >> that TCK is running at a maximum of 1/6th the system clock 
frequency if
> >> only 1 JTAG synchroniser is implemented in the system."  
> 
> I use both the Adaptive clocking (RTCK) and fixed freq on my 
JTAGjet.  It does both equally well.
> 
> >> For example using proper speed cabling 
> >> and including simple RC filters to reduce signal crossover at 
> >> high speeds near part pins.
> > No, you're completely wrong here.  The factors are part of the 
JTAG
> > design on the part, as the above link shows.
> 
> Correct.  I have actually tried attaching caps on the JTAG header 
pins and nothing I did made any difference on the 4MHz speed 
limitation.

I am sorry but I don't regard this as conclusive.

John Heenan