3. Configuring the Hardware
The TPL sniffer exposes a set of connectors on two sides. One side is dedicated to the ETPL bus connection and on the other side all other connectors are present. The two sides are galvanically isolated from each other: the ETPL bus connectors are isolated from all other accessible points on the housing.
3.1 Connecting to the ETPL Bus
The ETPL connectors are located on one side of the housing and are marked TPL_IN and TPL_OUT with a polarity indication + and -. The correct polarity of the connection is mandatory for the proper functioning of the sniffer and, in most cases, also for the system to be sniffed.
Conversely, the terms IN and OUT are conventional and the two connectors are electrically in parallel inside the TPL sniffer. They are physically duplicated to make it easier to connect the wires in certain use cases. For example, in the case of a daisy chain, the original ETPL bus is cut and the two ends must be plugged onto the receptacles of the TPL sniffer. In other cases, for example, when the ETPL bus has only one differential end available for connection to the TPL sniffer, there is no difference between the TPL_IN and TPL_OUT connectors, as long as the polarity is respected.
As a rule, if a stub is created from the original ETPL bus, its length should be as short as possible.
3.2 Optional ETPL Bus Loading
The TPL sniffer is designed to add minimal load to the ETPL bus by default. Therefore, it does not add any termination
impedance and the differential load seen from the bus is that of an input impedance of the MC33664 reflected on the
high voltage side by the 1:1 ratio T1 isolation transformer.
In case an interface other than the default one is desired; some settings are possible on the PCB:
- The two jumpers
JP2 located on the bottom side, should be closed (with a drop of
solder) in case a standard 150 Ω termination is desired.
- Additional component footprints are available on the top side of the PCB to accommodate different loads on the TPL
bus interface. These are
R13 (default DNP) and
R15 (default 0 Ω).
3.3 Power and Data Connections
The side of the case opposite the ETPL connectors has all the other available connectors of the TPL sniffer.
- The GND banana plug: used to connect, if necessary, the GND of the TPL sniffer to another potential. It is labeled
J5 in the schematics. In some cases of use, the whole system including, for example, the TPL sniffer,
the power supply, the logic analyzer and the associated PC, could be an electrically floating block. This connector
allows, if desired, the ground potential of the system (for example, the TPL sniffer and anything else that has its
ground connected to the TPL sniffer ground) to be set to any other convenient potential, that is, the protective
earth or the vehicle chassis ground (KL31).
- The data-out 8-pin connector: buffered SPI signals to be routed to the logic analyzer. It is labeled
J3 in the schematics.
- The power-on LED indicator UM11650 All information provided in this document is subject to legal disclaimers. ©
NXP B.V. 2021. All rights reserved. User manual Rev. 1 — 29 July 2021 7 / 14 NXP Semiconductors UM11650
- The USB Micro-B connector: to connect to a 5.0 V source. It is labeled
J4 in the schematics.
3.4 Connecting to the logic analyzer
The data output connector (
J3) is an 8-pin 4x2 male connector used as an interface to the logic analyzer, to transfer
TPL messages converted to SPI format.
The signals are all unidirectional and their direction is from the TPL sniffer (output) to the logic analyzer
The TPL sniffer is designed such that the cable connection to the logic analyzer can be relatively long, with a
maximum length of 2 m, without loss of signal integrity and therefore maintaining the logic and timing information.
This statement is only true if the following two rules are both satisfied:
- The cable used for the connection must have a characteristic impedance of 100 Ω. This is the impedance normally
found on standard IDC ribbon cables.
- The logic analyzer side of the cable should only be loaded with high impedance terminations such as a High-Z input
from an oscilloscope, for example, 15 pF || 1 MΩ, or 5 pF || 10 MΩ (better), or digital inputs from a logic analyzer
(for example, 10 pF || 2 MΩ).
Failure to follow these rules does not guarantee proper operation of the TPL sniffer, unless the cable length is
considerably short (< 15 cm) so that reflections in the cable can be neglected.
For signal integrity and EMI reduction, the data lines are interleaved with the ground potential with the pinout
described in Table X.
The TPL sniffer data output lines and the ETPL inputs are internally protected by ESD suppression devices.
Nevertheless, standard electrostatic precautions should be taken when handling and using the TPL sniffer.
The pin assignment for the data output connector is described in the following table:
||SPI interrupt signal
||SPI bus clock
||SPI bus data
||SPI chip select
The supplied 8-pin connection cable should be plugged into the ANALYZER connector with the blue wires on top (NXP
logo side) and the black wires on the bottom.
3.5 Interfacing with the Saleae Logic Analyzer
The supplied 8-pin connectors cable is fitting the Saleae Logic 8 and Logic Pro 8/16 analyzer series input
connectors. To connect to the Saleae Logic Analyzer, the cable should be plugged with the blue wires on top (Saleae
logo side) and the black wires on the bottom.
Saleae provides a software interface with its product to help decode the acquired signals. To learn more, visit the
Plug-ins and extensions for the Saleae Logic Analyzer software are available to decode TPL frames. Visit section 4 for more details.
3.6 Powering the TPL sniffer
The TPL sniffer can be powered through the USB Micro-B connector (J4, labeled PWR) by a 5.0 V source with 50 mA (average) and 150 mA (peak), typically a USB power bank or a USB cable connected to a computer.
3.7 Power bank keep-alive function
The purpose of the keep-alive feature is to avoid the activation of the automatic shutdown feature found on most consumer USB power banks. Such a shutdown would likely occur due to the limited power consumption of the TPL sniffer circuit alone, in the 10 mA to 20 mA range. Therefore, the sniffer activates an additional 150 mA of internal power consumption with a period of 5.8 seconds and a duty cycle of 20 % (all figures are approximate). This simulates a load large enough to keep most power banks energized.
If the power-on LED indicator goes out shortly after the TPL sniffer is first powered up with a power bank, consider trying another power bank model.