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TapNLink User Manual

Introduction

This documentation covers details that are not covered in the Getting started.

Electrical connections

This section describes the TapNLink 'NFC + BLE' electrical interface, which connects the Tap to the target.

Connectors

The module TapNLink BLE-NFC has 3 connectors:

  • J1 (2x5 in 1.27mm steps) that connects the TAP to the debug connector (ARM-SWD standard) of the target card via a flex cable (in 0.635mm steps).
  • J3 (1x5 in 2.54mm steps) which connects the TAP to the target board more flexibly by free wires not necessarily grouped in tablecloth. Note that J3 is a subset of J1.
  • P1 extension connector, composed of two rows P1A and P1B of contacts in 2mm steps. This connector is mainly reserved for the addition of expansion cards and will only be briefly described in this document.

The following figure shows (bottom view) the signals connected to J1 and J3:

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J1 pinout

This connection corresponds to the format specified by ARM for Cortex-M microcontrollers debug port.

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The names in parentheses correspond to the JTAG protocol. In general, it is advisable to prefer SWD to JTAG on Cortex-M microcontrollers. For any other microcontroller, use the S3P protocol.

The signals to be connected in SWD or S3P are:

  • Gnd
  • Vcc (the target must provide the TAP power),
  • SWDIO: Bi-directional data signal.
  • SWDCLK: Clock signal, bi-directional in S3P.
  • NRST: Reset signal of the target processor. Its connection is optional. It should be maintained if you want to use the reset command, or if you want to use the TAP as a programmer (the reset signal is required in some programming situations).

J3 pinout

J3 was added for practical reasons. The 2.54 mm step connectors are cheaper and more robust and can connect to a wide range of connectors. J3 does not correspond to a standard but connects easily to the 20-point ARM 2.54 mm-step standard and contains the main signals necessary for S3P and SWD protocols:

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P1 extension connector

P1 extension connector is composed of two mechanically independent parts:

  • P1A has 8 points
  • P1B has 8 + 2 = 10 points. The two additional points are used exclusively for initial programming.

Most of the signals on the expansion connector are reserved for extensions proposed by IoTize, so this connector will only be used in exceptional situations, for example, if it is necessary to control the reset of the TAP.

The figure below shows a top view of P1 with the TAP's power, reset and wakeup points.

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Electrical characteristics

On the TAP side, the signals are connected to the main microcontroller via a 22 ohm resistance:

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The power source is itself lowered (typically 250 mV drop) by a diode (NSR20F30) to allow NFC to provide the power supply.

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The applicable voltage levels are those of the main MCU (STM32L432K):

Symbol Parameter Min Typ Max Unit
Vtarget(1) Voltage supplied by target 2 3 3.5 V
VIL I/O signals input low level - 0.3xVcc(2) V
VIH I/O signals input high level 0.7xVcc(2) 0.4 V
VOH Output high level voltage for I/O signals 0.65xVcc - V
VOL Output low level voltage for I/O signals - 0.35xVcc
ICC Current supplied by target 10mA 15mA 18mA mA
  1. Vtarget is the voltage supplied by the application board (the target) at the J1/J3 connector.

  2. VCC is the TAP voltage (typically Vcc = Vtarget – 250mV).

Cable and connectors selection

The cable between the Tap and the application board should be as short as possible. We highly recommend to use a target cable of much less than 1 meter.

Tests have been done in SWD protocol connecting an application board populated with an STM32 and a TAP using a ribbon cable on J1: no problems occurred with a length up to 1 meter. Depending on the length and the environment, you must guard against electromagnetic interference. In an aggressive environment, you may have to use a shielded cable.

Mechanical connections

This section describes how to physically connect the TapNLink to the target.

The TapNLink can either be used by itself, or be clipped into an IoTize Cup (see image) and used in proximity to the target.

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Connection constraints

  • Antennas (NFC, BLE or Wi-Fi): Avoid having metal screens (Faraday cages) between the smartphone and the Tap. Avoid proximity with any metal which may disturb the electromagnetic field.
  • The smartphone NFC antenna must be placed close to, and parallel and centered with, the TAP NFC antennae. Smartphones/tablets vary greatly in size and in the position of their NFC antenna. Generally, smartphone NFC communication is optimal at a distance of 10 mm, and can be problematic at 30 mm.
  • The TapNLink electronics must be protected from electrostatic discharge, and corrosive environments.
  • The connection cables should be kept away from electromagnetic disturbance (motors,...).

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The TapNLink PCB does not have screw holes. When used without a Cup box, it must be fixed either by:

  • gluing
  • snaps applied to the outer perimeter or to the central slots (in the same way as the Cup box),
  • elastic tape inserted in the two central slots,
  • metal screws (M1.6) in the central slots, with insulating washers between the screw head and the PCB to avoid contact with the extension connector.

IoTize Cup box

It is recommended to put the TapNLink inside an IoTize Cup box which resolves the connection constraints. The minimum order quantity is 50 boxes.

The Cup box can be supplied with optional items or a customized color:

  • A flat or double-sided adhesive gasket to waterproof the support's joint,
  • A Bluetooth logo decoration which could be glued to the outside of the case.
  • The Cup box color can be customized if more than 2000 boxes are ordered. Simply request a quotation from IoTize.

The customer could manufacture a specific label (dimensions are given below).

If required, the customer must provide 3mm diameter screws best suited to their support.

Cup dimensions:

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Placement of the Tap in the Cup

The tap should be correctly positioned over the tap connectors and snapped into the CUP.

Caution: The guide marker must be correctly positioned for the ceramic antenna.

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This exploded view shows the Tap and Cup fitting:

  1. Customized label (optional) which may indicate connection modes (BLE, Wi-Fi,...). The center of the label corresponds to the center of the NFC antenna.
  2. Cup case, in ABS.
  3. Tap, see previous section for details.
  4. Fixing screws (not supplied) to be chosen according to the support wall.
  5. Optional gasket (double-sided adhesive or silicone gasket).

Placement of CUP on support wall

The CUP can be mounted on the inside or outside of the support wall.

Outside or inside mounting

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An inside mounting requires a 50mm diameter hole in the support wall which will be visible so must have a neat finish. It is attached with either screws or a double-sided adhesive seal. If fastening screws are used:

  1. Mark the center of the CUP on the support wall.
  2. Drill the screw holes (3.2mm diameter) on a diameter of 56.5mm from the center of the CUP, on the same horizontal as the center.
  3. Drill the main hole (50mm diameter) using a bit saw.

An outside mounting requires a smaller hole in the support wall (for the passage of the cable and its connector), and requires holes for two fixing screws, made in the same way as for an inside mounting. The size and shape of this hole depends on which connector is used, J3 or J1.

  • J3 simplified connector (1x5 points) 2.54mm step (e.g. Molex 0705430004). Recommended for wide range of connections, very low cost of connectors, better robustness.
  • J1 complete connector (2x5 points) 1.27mm step (for a flex cable with 0.635mm step). Recommended when the target application has the same type of connector, and to use the JTDI/JTDO signals that are absent from the main connector.

The connection can be vertical or horizontal depending on:

  • congestion constraints (horizontal is more compact),
  • waterproofing requirements,
  • locking system requirements on the connectors.

Waterproofing or sealing

If the Cup is used as a receptacle for an elastomeric resin (silicone elastomer system specially designed for electronic potting application), a vertical connection is preferable to allow easy connection/disconnection of the TAP without the resin needing to be modified.

Hardware factory reset

This section describes how to perform a hardware factory reset and recover IoTize default configuration.

  • If you lose the administrator password, you can no longer change your Tap's configuration.
  • In this case, you must erase the current configuration and recover the factory configuration using the hardware factory reset procedure, presented here.
  • This feature can be disabled in IoTize Studio from menu IoTized Application\Tap\Configuration Access control\By hardware signal but it is strongly advised to keep the default value 'Yes' (otherwise reconfiguration won't be possible).

A pad on the PCB of your Tap must be linked to ground during power-on before performing a factory reset:

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  1. Power off the module.
  2. Connect the HW_FR signal (P1.2) to the ground (P1.9) and keep them connected.
  3. Power on the module.
  4. Wait for 10 seconds.
  5. Power off the module.
  6. Disconnect the HW_FR.
  7. Power on the module again: the default configuration is reloaded.

A pad on the PCB of your Tap must be linked to ground during power-on before performing a factory reset:

  1. Power off the module,
  2. Connect the pad to the ground (see below for details of 10pt/5pt modules),
  3. Power on the module,
  4. Wait for 10 seconds,
  5. Power off the module,
  6. Disconnect the pad,
  7. Power on the module again: the default configuration is reloaded.
SWD 10-point connector modules SWD 5-point connector modules
Connect pad P1 to GND (pin 7 connector J2) Connect pad P2 to GND (pin 7 connector J2)
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The hardware factory reset is not available on these modules.