Specifications

Table Of Contents
ARM Debugger 79 ARM specific SYStem Commands
©1989-2014 Lauterbach GmbH
SYStem.JtagClock Define JTAG frequency
Default frequency: 10 MHz.
Selects the JTAG port frequency (TCK) used by the debugger to communicate with the processor. This
influences e.g. the download speed. It could be required to reduce the JTAG frequency if there are buffers,
additional loads or high capacities on the JTAG lines or if VTREF is very low. A very high frequency will not
work on all systems and will result in an erroneous data transfer. Therefore we recommend to use the default
setting if possible.
<frequency>:
The debugger can not select all frequencies accurately. It chooses the next possible frequency and displays
the real value in the “System Settings” window.
Besides a decimal number like “100000.” also short forms like “10kHz” or “15MHz” can be used. The short
forms implies a decimal value, although no “.” is used.
RTCK: The JTAG clock is controlled by the RTCK signal (Returned TCK).
On some processor derivatives (e.g. ARMxxxE-S) there is the need to synchronize the processor clock and
the JTAG clock. In this case RTCK shall be selected. Synchronization is maintained, because the debugger
does not progress to the next TCK edge until after an RTCK edge is received.
In case you have a processor derivative requiring a synchronization of the processor clock and the JTAG
clock, but your target does not provide a RTCK signal, you need to select a fix JTAG clock below 1/6 of the
processor clock (ARM7, ARM9), below 1/8 of the processor clock (ARM11), respectively.
When RTCK is selected, the frequency depends on the processor clock and on the propagation delays. The
maximum reachable frequency is about 16 MHz.
Example: SYStem.JtagClock RTCK
Format: SYStem.JtagClock [<frequency> | RTCK | ARTCK <frequency> | CTCK <fre-
quency> | CRTCK <frequency>]
<frequency> 4kHz100 MHz
1250000. | 2500000. | 5000000. | 10000000. (on obsolete ICD hardware)
The clock mode RTCK can not be used if a DEBUG INTERFACE (LA-7701) or
a debug cable with 14-pin flat cable (LA-7740) is used. And it is required that
the target provides a RTCK signal.