General Pcb Layout Guidelines - IAR SYSTEMS I-jet User Manual

Such SI tools will take into consideration the output impedance and rise and fall times
of the MCU trace port lines, the length, geometry, and impedance of the PCB traces, the
geometry of the layer stack as well as the dielectric properties of the PCB materials to
give a simulated graph of the resulting waveform at the trace connector or any other
place along the path.
If the resulting waveform is distorted, most simulation tools will help to determine the
optimal series termination resistor for each trace line.
Important: All trace data lines and trace clocks must have a series resistor placed near
the MCU source pin. The resistor value will be determined by the simulation tools or
can be found experimentally by examining the live signal with an oscilloscope at the
trace connector.

GENERAL PCB LAYOUT GUIDELINES

4-bit ETM trace
Cortex-M devices have only a 4-bit ETM trace port. These trace signals must be routed
to the standard 0.05 in × 0.05 in (1.27 mm × 1.27 mm) MIPI-20 connector header.
The recommended part number for a 4-bit ETM+JTAG debug connector is
SHF-110-01-L-D-SM by Samtec or any other compatible shrouded header. The header
should be positioned relatively close to the MCU—not more than 3 inches (75mm)—so
that the even pins face the MCU as they have active signals on them.
16-bit ETM trace
Most Cortex-R and Cortex-A devices come with a 16-bit trace port. To accommodate
faster speeds, the signals must be connected to a 38-pin Mictor connector, making sure
the track lengths from the MCU are matched to be within 0.5 inches (12.5 mm) to
minimize signal skew.
The recommended part number for a 16-bit ETM+JTAG debug connector is 5767110-1
from AMP/Tyco.
The Mictor connector is designed to carry high-speed signals (10 Gb/s) and has a
characteristic impedance of 50 Ohm. To eliminate signal distortion, the ETM trace
signals on PCB must also have 50 Ohm impedance. The connector should be placed
relatively close to the MCU—not more than 3 inches (75mm).
PCB routing
These are useful hints for PCB routing:
Use series termination
●
Place a series resistor on each trace signal near the source (MCU).
I-jet Trace
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