
PPC600 Family Debugger | 8
©
1989-2022
Lauterbach
Target Design Requirement/Recommendations
General
•
Locate the JTAG / COP connector as close as possible to the processor to minimize the
capacitive influence of the trace length and cross coupling of noise onto the JTAG signals. Don’t
put any capacitors (or RC combinations) on the JTAG lines.
•
Connect TDI, TDO, TMS and TCK directly to the CPU. Buffers on the JTAG lines will add delays
and will reduce the maximum possible JTAG frequency. If you need to use buffers, select ones
with little delay. Most CPUs will support JTAG above 50 MHz, and you might want to use high
frequencies for optimized download and upload performance.
•
Ensure that JTAG HRESET is connected directly to the HRESET of the processor. This will
provide the ability for the debugger to drive and sense the status of HRESET. The target design
should only drive HRESET with open collector/open drain.
•
For optimal operation, the debugger should be able to reset the target board completely
(processor external peripherals, e.g. memory controllers) with HRESET.
•
In order to start debugging right from reset, the debugger must be able to control CPU HRESET
and CPU TRST independently. There are board design recommendations to tie CPU TRST to
CPU HRESET, but this recommendation is not suitable for JTAG debuggers.
•
If the processor does not have QACK/QREQ pins, leave the corresponding pins on the debug
connector N/C.
•
If the processor has QACK/QREQ pins, QACK must be LOW in order to halt the core for
debugging. If QACK is connected to the debug connector, the debugger can drive it LOW by
command. If QACK is not connected to any system controller, it is recommended to tie it to GND.
•
The debug cable uses VCCS on the JTAG-VREF pin to generate the power supply for the JTAG
output buffers. The load on the JTAG-VREF pin caused by the debug cable depends on the
debug cable version:
Gray
ribbon
cable
The VCCS pin is used as reference voltage for the internal power supply
in the debug cable. This causes a load of about 50 k
. It is
recommended to use a resistor with max. 5 k
to VCC, and max 1 k
for
systems with VCCS = 1. 8V
Blue
ribbon
cable
The VCCS pin should be connected to VCC through a resistor with max.
10
, as the output buffers are directly supplied by the VCCS pin.