
XETK-V2.0 - User’s Guide
31
ETAS
Hardware Description
The ECU part of the XETK-V2.0B Nexus (JTAG) interface is depicted in Fig. 4-13.
For proper operation of the XETK-V2.0B it is mandatory to provide impedance
matched series termination resistors on the ECU pcb for the signals TDO and /
RDY (if available). If trace measurement is used it is mandatory to provide imped-
ance matched series termination resistors on the ECU pcb for the signals /EVTO,
MCKO, MDOx, and /MSEOx.
The ECU specific impedance matched series termination resistor values (e.g.
22 Ohm, 33 Ohm, 50 Ohm, or other) must be chosen with the consideration to
match the source impedance to the cable impedance. The ETAHx cables used
between the microcontroller and XETK-V2.0B have a 50 Ohm impedance.
The XETK incorporates 44 Ohm series resistors for the TDI, /TRST, TCK, and TMS
lines on the ECU interface. Additional pull ups / downs are as shown.
4.10
Watchdog Timer Disable / Tool Detect Interface
The XETK-V2.0 provides a method to disable an external watchdog timer (WDT)
circuit on the ECU.
4.10.1
XETK-V2.0A/C
The watchdog disable control signal is available on the VertiCal connector on
signal TOOL_IO2 (pin N22). This signal is routed directly to a ball of the BGA
VertiCal Base Board, completely bypassing the microcontroller on the VertiCal
Base Board. The ECU receives the signal on the TOOL_IO2 optional ball. Each
microcontroller package has a unique ball number for TOOL_IO2, see Fig. 4-14
for listing of ball numbers and package information.
When the XETK-V2.0A/C is configured to use this signal (configuration parame-
ter "ECU Watchdog Control" set to "Disabled"), the signal TOOL_IO2 is set to
logic high. Logic high is defined within the section "Electrical Characteristics"
on page 56. When "ECU Watchdog Control" is set to "Enabled" the TOOL_IO2
pin is set to logic high when the debugger requests that the watchdog is
enabled, else the pin is not driven (high-Z). When the "ECU Watchdog Control"
is set to "Controlled by ECU", the TOOL_IO2 pin is not driven by the XETK-
V2.0A/C (high-Z), regardless of the debugger request.
CAUTION!
Risk of damaging the XETK due to short circuiting the JTAG
signals!
When the XETK-V2.0B is connected to the ECU, you must ensure that
no other device is actively driving the JTAG signals (TCK, TDI, TMS) via
another connector on the ECU (e.g. Lauterbach debugger directly on
ECU pcb). To use these other tools you must remove the XETK-V2.0B
or plug the other tools into a debugger arbitration board.