Lpc2000

Hi Arie,

I would agree that the RTCK is useful. This thread started when someone 
wanted to throw away JTAG pins. I would throw away TRST (tap reset - 
which can be done via JTAG) rather than RTCK.

Regards
Michael

>From: "Michael Johnson"
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>>The RTCK isn't strictly needed. Without the RTCK if the JTAG port works
>>slowly, as is the case of the LPC2xxx, then the JTAG cable/debugger has
>>to put in a delay before it samples the TDO. I'm surprised that
>>companies are selling JTAG cables that require RTCK - the cynic in me
>>says it's a way of getting repeat business.
>>    
>>
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>AFAIK:
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>(1) Use of RTCK for PLL'ed MCUs.
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>It is extremely useful when you have an MCU that starts at a slow speed,
>then turns on a PLL and speeds up. The RTCK then continuously indicates the
>speed at which you can clock instructions into the core and the JTAG can
>track that speed.
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>Normally in setups like this the PLL registers are programmed first, then
>the RAM is uploaded. The increase in upload speed is equal to the PLL
>multiplier.
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>(2) Use of RTCK to synchronize JTAG to the core execution.
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>When you don't know the core clock you may have to wait a few CLK states
>after loading each instruction into the pipeline so you are sure it is
>executed before the JTAG sends in the next instruction.
>By using RTCK you can syncronize this process and skip a few waitstates.
>
>
>Regards,
>Arie de Muynck
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