3.3.3. TCK and TCKEN

TCK is the master clock for the ETM7 JTAG interface. TCKEN is a synchronous clock enable signal.

In a system with an ARM7TDMI or ARM720T, TCK is generally a free-running clock, asynchronous to CLK. In such a system TCKEN must be tied HIGH.

In an ARM7TDMI-S system there is a single clock used as both the main system clock, and the JTAG clock. In this case you must connect the single main clock to both CLK and TCK. You can then use TCKEN to control the JTAG interface.

ETM7 is designed to function with fully asynchronous CLK and TCK inputs. Synchronizing logic is included in the design to prevent metastability problems between the two clock domains when running with asynchronous clocks.

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