UG569: Adapter Board for Co-processor Expansion Kit User's Guide

1. Introduction

The Adapter Board for Co-processor Expansion Kit is an excellent way to explore and evaluate co-processor radio boards with various host devices using either SPI or SDIO interfaces. Examples of host devices include EFM32 or EFR32 devices, Raspberry Pi, or other Linux machines with an SDcard interface, and STM microcontrollers.

When connected to a compatible host board, the Adapter Board enables direct communication between the Wi-Fi Network or Radio Co-Processor (NCP/RCP) board and the host device, ensuring correct operation during debugging.

The kit is available in three variants: Si-EB8045A, Si-EB8045B, and Si-EB8045C. These variants integrate seamlessly and provide additional wireless connectivity to compatible Silicon Labs Wireless Pro Kit Mainboards via the EXP header, Raspberry Pi via the HAT interface, and other host boards equipped with an Arduino UNO rev 3 compatible host interface, such as STM32 Nucleo-64 boards.

Adapter Board Common Features:

• Device Interface: Silicon Labs Wireless Radio Boards
• USB port for In System Programming (ISP) of SiWx91x Devices
• Power Source Selector
• 2x analog Current Sense outputs with different gains
• Reset button
• Breakout pads

BRD8045A Features:

• Silicon Labs EXP interface for EFM32 or EFR32 Devices Wireless Pro Kit
• EXP-MicroSD Adapter Board (BRD8046A) for other Linux machines (SDIO)
• SiWx917-EB4346A
• Si-EB8045A

BRD8045B Features:

• HAT compatible interface for Raspberry Pi
• Si-EB8045B

BRD8045C Features:

• Arduino UNO rev 3 compatible Shield interface for boards such as STM32 Nucleo-64
• Si-EB8045C

Figure 1.1: Image showing the Silicon Labs BRD8045A Adapter Board connected to a Silicon Labs Wireless Pro Kit Board.

Figure 1.2: Image showing the Silicon Labs BRD8045A Adapter Board connected to a Silicon Labs EXP-MicroSD Adapter Board.

Figure 1.3: Image showing the Silicon Labs BRD8045B Adapter Board connected to a Raspberry Pi.

Figure 1.4: Image showing the Silicon Labs BRD8045C Adapter Board connected to a NUCLEO-F411RE.

1.1 Ordering Information

The following table details the ordering information for the adapter board variants.

1.2 Prerequisites and Compatibility

Prerequisites

To function correctly, the Si-EB8045x Adapter Board for Co-processor Expansion Kit requires a compatible host board and a Silicon Labs' co-processor radio board.

The different variants of the Adapter Boards are designed for interfacing with various types of host boards. As the Adapter Board either uses or replicates the host power supply, a host board must always be connected during operation.

Hardware Compatibility

The following table provides an overview of the board variants and their compatible hardware.

Note 1: The Wireless Pro Kit Mainboard needs to be combined with a radio board (host) to work in this context.

Note 2: Using the SDIO interface mapped to the HAT connector of a Raspberry Pi 3 might limit the use of other on-board modules.

Any Silicon Labs Starter Kit or Wireless kit can be used. However, some specific kits might have shared functionality mapped to the EXP header (refer to section EXP Header Pinout). Users are encouraged to check the connectivity of SPI INTR and SPI CS before selecting a Starter Kit or a radio board.

Note that while the Si-EB8045B offers some functionality with an EFR32 radio board when connecting the SPI interface to the Raspberry Pi processor via the HAT interface, the Si-EB8045A and Si-EB8045C will not work with EFR32 radio boards used as NCP.

2. Specifications

2.1 Recommended Operating Conditions

The following table serves as a guideline for the correct use of the Adapter Board for Co-processor Expansion Kit, indicating typical operating conditions and some design limits.

Note 1: Current availability varies linearly with the Voltage supplied at VVMCU.

2.2 Operating Characteristics

The following table provides typical performance figures for the Adapter Board.

Current Sense High Gain Operating Characteristics

Current Sense Low Gain Operating Characteristics

3. Hardware Overview

This section provides an overview of the Adapter Board hardware. While the power architecture and device interface towards co-processor radio boards are common to all BRD8045x variants, the host interface differs based on the host board type. Refer to the Ordering Information section for available variants and part numbers. All host interfaces feature a high-speed communication port (SPI or SDIO) for exchanging wireless data packages, remote reset, and other signals specific to the host board interface. Connector pinout details are covered in the Connectors chapter.

3.1 Block Diagram

The figure below illustrates the Adapter Board's block diagram. Common features are shown in blue blocks, while different, mutually exclusive interfaces are in grey blocks. SPI/SDIO lines are blue, UART lines are white, host and device power domains are black, and board power is grey.

Figure 3.1: Kit Block Diagram. The diagram shows various host boards (Linux Host, Raspberry Pi Host, STM32 Host, WSTK/WPK) connecting to the BRD8045x Adapter Board through different interfaces like SDIO, RPi HAT, EXP Header, and USB-UART Bridge. The adapter board includes components like a 5V Automatic Voltage Selector, UART Switch, Power Mode Switch, HG/LG Current Sense Analog Outputs, and connects to a Co-processor Radio Board.

3.2 Communication and Signal Mapping to Host Interfaces

The BRD8045x Adapter Board exposes the device's communication ports on its host interfaces. For SiWx91x Wi-Fi co-processors, SPI/SDIO signals are routed through a resistor matrix to determine the path to a specific host interface. This guide details factory configurations, but users can modify hardware by soldering/desoldering components. Schematic and assembly drawings are available at silabs.com.

The table below summarizes the signals routed to the host interface for each product variant, relevant to both co-processor and SoC radio boards:

The BRD8045B Adapter Board for Raspberry Pi also supports SPI communication with Silicon Labs Multiprotocol Systems on Chip of the EFR32 device family.

3.2.1 UART and USB connections

The Adapter Board's UART data lines are factory-mapped to the SiWx91x Wi-Fi co-processor's UART port for ISP mode. A slide switch allows users to connect this port either to the host for remote programming or to the on-board UART-USB bridge for PC connection and firmware loading via a terminal.

While variants do not natively support UART with other EFR32 devices, shunt resistors allow hardware remapping of the UART port for EFR32 or other SiWx91x Systems on Chip. Schematic and assembly drawings are available at silabs.com. UART data lines for both SoC and co-processor are accessible via breakout pads (BO104-BO105 for SoC RX/TX, BO102-BO103 for NCP/RCP RX/TX).

The Adapter Board offers three modes:

• USB: Factory default; UART peripheral connected to the UART-USB bridge.
• NC: Disconnects UART data lines, allowing external UART device connection via breakout pads.
• HOST: Connects the co-processor board to the host's UART peripheral.

Figure 3.2: UART Slide Switch. This diagram illustrates the connection paths for UART communication, showing the USB Type-C Connector, USB-to-UART Converter, Raspberry Pi Connector, Expansion Header, and Shield Connector, all leading to the Co-Processor Radio Board via a slide switch controlling USB, NC, or HOST modes.

3.2.2 Reset Button

The RESET button can be used to reset the target device on the Radio Board (active low). When used with an STM32 Nucleo-64 board (BRD8045C), the reset circuit resets both the host and device simultaneously. The host can also reset the device remotely without resetting itself.

3.3 Power Supply and Current Sense Outputs

This section details the hardware architecture of the BRD8045x Adapter Board regarding power supply and current sense outputs. For more in-depth information, refer to Chapter 5 (Power Supply) and Chapter 6 (Current Measurements).

The Adapter Board requires a 5V power source for operation, powering analog circuits like voltage buffers and power switches. Power is supplied via the host interface or the USB connector. A power multiplexer automatically selects the power rail, prioritizing USB power if available and within the specified voltage range (greater than 4.4V).

A power switch allows users to select the power mode, which dictates how the co-processor (Device) is powered. This switch controls power transistors that close current paths, requiring the 5V rail. More details on power modes are in Section 5.2 (Device Power Options).

The on-board buffer circuit tracks the host voltage and provides power to the co-processor. It also offers two analog outputs with different gains for tracking current consumption. Details are in Section 6.1 (Analog Outputs).

3.4 Hardware Layout

The physical implementations of the BRD8045x Adapter Boards are shown below. Dashed areas indicate unmounted components.

3.4.1 Hardware Layout of BRD8045A

The BRD8045A Adapter Board has components on the top side only.

Figure 3.3: BRD8045A Adapter Board Hardware Layout. This figure shows the top and bottom views of the BRD8045A board, highlighting key components such as the Power Switch, EXP Header, Power Indicator, UART Switch, Radio Board Connectors, Reset Button, and USB Connector.

3.4.2 Hardware Layout of BRD8045B

The BRD8045B Adapter Board is designed to mount on a Raspberry Pi using the HAT connector (bottom view). M2.5 mounting holes are provided for securing the board to the Raspberry Pi host with optional spacers.

Figure 3.4: BRD8045B Adapter Board Hardware Layout. This figure displays the top and bottom views of the BRD8045B board, indicating the Power Switch, Power Indicator, UART Switch, Radio Board Connectors, Reset Button, USB Connector, and Raspberry Pi Connector, along with Raspberry Pi M2.5 Mounting Holes.

3.4.3 Hardware Layout of BRD8045C

The BRD8045C Adapter Board is designed to mount on an Arduino UNO rev 3 compatible host board, such as STM Nucleo-64 boards, using four pin headers (bottom view).

Figure 3.5: BRD8045C Adapter Board Hardware Layout. This figure shows the top and bottom views of the BRD8045C board, featuring the Power Switch, EXP Header, Power Indicator, UART Switch, Radio Board Connectors, Shield Interface, Reset Button, and USB Connector.

4. Connectors

This chapter provides an overview of the Adapter Board's connectivity options for Co-processor Radio Boards.

4.1 Radio Board Connectors

Co-processor radio boards connect to headers located on the right side of the Adapter Board, with the antenna pointing outward and to the right.

4.2 USB Type-C Connector

The USB Type-C connector, located on the bottom right corner, provides auxiliary power and access to the UART peripheral via a built-in USB bridge, typically used for firmware downloads to co-processors.

4.3 EXP Header

A right-angle, female, 20-pin EXP header is provided for connection to a Wireless Pro Kit. This header follows a pinout that ensures proper interface of common power nets and peripherals for protocols like SPI and UART. It also exposes signals specific to SiWx91x Wi-Fi co-processors, such as PTA, Low-power Handshake Sleep/Wake Up, and RESET. For detailed pinout information on specific Wireless Pro Kits, consult their respective user guides.

Alternatively, when connected via a BRD8046A EXP-MicroSD Adapter Board, the EXP header exposes the SDIO peripheral to Linux machines with an SDcard reader. This connection does not provide power, requiring a USB Type-C cable for power.

The figure below illustrates how SiWx91x Wi-Fi co-processor peripherals are mapped to the EXP header.

Figure 4.1: Expansion Header. This diagram shows the 20-pin EXP header pinout, detailing signals like BOARD_ID_SDA, BOARD_ID_SCL, SDIO D3, PTA GRANT, SPI INTR/SDIO D2, #RESET, WAKEUP, SLEEP, PTA PRIORITY, PTA REQUEST, GND, and their corresponding functions and connections to the Radio Board I/O, Power, and Ground.

4.3.1 EXP Header Pinout

The table below lists the pins and functions of a SiWx91x co-processor mapped to the EXP header. Note that some pins are shared with other functions on the Wireless Pro Kit mainboard. For a complete description, refer to UG573: Si-MB4002A Wireless Pro Kit Mainboard User's Guide.

Note 1: SPI signals map to a subset of pins used for SDIO in SiWx917 chips. When using the BRD8045A EXP Adapter Board with a Wireless Pro Kit, the EFR32 host connects via SPI. With the BRD8046A EXP-MicroSD Adapter Board and a generic host's SD card slot, the connection is via SDIO.

4.4 Raspberry Pi Connector (HAT)

The Raspberry Pi connector (HAT) is located on the bottom side of the Adapter Board. The figure below shows how the SiWx917 Wi-Fi co-processor peripherals are mapped to the Raspberry Pi Connector.

Figure 4.2: Raspberry Pi Connector (HAT). This diagram illustrates the pin mapping for the Raspberry Pi HAT connector, detailing signals like 3V3, 5V, GND, GPIO pins, and their functions such as UART, SPI, SDIO, RESET, WAKEUP, SLEEP, and HAT device identification.

4.4.1 Raspberry Pi Connector (HAT) Pinout

The table below lists the pin assignments of the Raspberry Pi connector and the peripheral functions available on the Adapter Board.

4.5 Shield Interface

The Arduino UNO rev 3 compatible Shield interface consists of four pin headers on the bottom side of the Adapter Board. The figure below shows how the SiWx917 Wi-Fi co-processor peripherals are mapped to an Arduino-compatible host board, such as an STM Nucleo-64 (right). The location of the Shield Interface connectors is shown from the top side for easier probing, while the connectors themselves are on the bottom side.

Figure 4.3: Shield Interface. This diagram shows the pinout for the Shield Interface connectors (P101, P102, P103, P104) on the Adapter Board, detailing their mapping to STM Nucleo 64 pins and co-processor functions like SPI, UART, RESET, WAKEUP, SLEEP, and ISP MODE.

Additionally, the Adapter Board includes pads for connecting to a N144 Complimentary SDIO interface, which links to the SDIO peripheral of a Nucleo 144 board (typically STM32H7 host). An extra connector (P105) must be soldered, and six shunt resistors moved, to divert signals from the co-processor Radio Board's SPI/SDIO peripheral to the SDIO pins. Users intending hardware modifications can find schematic and assembly drawings at silabs.com.

4.5.1 Shield Interface Pinout

The table below details the pin assignments of the Shield Interface and the peripheral functions available on the Adapter Board.

Bottom Row (P101) Pinout

Bottom Row (P103) Pinout

Top Row (P102) Pinout

Note: In BRD8045C Shield Adapter Board for Co-processor, the Reset Button resets both Host and Device.

Top Row (P104) Pinout

4.6 Breakout Pads

Breakout pads are through-hole pads grouped by function, typically located at board edges for probing signals and power rails. Pads within a cluster are arranged in rows spaced 2.54 mm apart, allowing optional pin header soldering. Locations are consistent across all board variants.

Figure 4.4: Overview of Breakout Pads. This figure provides a visual overview of the breakout pad clusters and their locations on the board, including Power, PTA, UART, Current Sense Amp Outputs, I2C, and Current Sense pads.

4.6.1 Power Breakout Pads

Located on the top left corner, these pads allow users to probe power rails.

Note 1: More details on the Adapter Board's power architecture are in Section Power Supply and Current Sense Outputs.

Note 2: VMCU is for sensing only; no voltage should be applied. It is generally not recommended to apply voltage to these pads while the Adapter Board is connected to a host board.

4.6.2 PTA Breakout Pads

4.6.3 Current Sense Amplifier Output Breakout Pads

These pads provide direct access to the on-board current sense amplifier for probing. They are usable in BUF MODE only, when the on-board voltage buffer supplies current to the device (co-processor). A 0.5 Ω resistor is connected between the positive and negative nodes.

Note: Refer to Section 6.1 Analog Outputs for current measurements using analog outputs.

4.6.4 UART Breakout Pads

While the host interface is mapped to the ISP UART (co-processors), these pads offer direct access to both ISP and VCOM UART (SoCs) simultaneously.

4.6.5 Current Sense Breakout Pads

These pads expose differential signals, positioned away from the board edge along the voltage buffer's current path to minimize noise. They are usable in BUF MODE only. A 0.5 Ω resistor connects the positive and negative nodes.

4.6.6 I2C Breakout Pads

These pads allow probing signals when SoCs are used instead of co-processors.

5. Power Supply

This section covers two key aspects of power supply: powering the Adapter Board and powering the co-processor radio boards attached to it.

5.1 Board Power Options

The Adapter Board requires a 5V power source to operate correctly.

When connected to a compatible Host Board, the 5V power is provided by the host board. A lit green Power Indicator LED signifies that the Adapter Board is powered by the Host Board.

If the Host Board cannot provide sufficient power, or when using an SDcard interface via BRD8046, auxiliary power must be supplied via a USB cable connected to the Adapter Board's USB connector. The USB power source should be adequate for the target application. A lit red Power Indicator LED indicates power from the auxiliary input. USB power takes priority over Host Board power if the voltage is greater than 4.4V.

Figure 5.1: Adapter Board Auxiliary Power Connector and Power Indicator. This image highlights the Power Indicator LED and the Auxiliary Power input connector on the Adapter Board.

If the Power Indicator is not lit, the Adapter Board is not powered and cannot operate.

Note: When using a WPK or STK, the power switch on the Mainboards must be set to AEM mode to supply 5V power to the Adapter Board. To power an EFR or EFM by battery, connect an auxiliary USB power source to the Adapter Board first.

5.2 Device Power Options

When correctly powered, the Adapter Board interfaces a Host and a Device on different boards, ensuring both communicate at the same voltage level. This prevents back-feeding between circuits and ensures accurate current measurements.

Power for the target device (SiWx917 or EFR32 co-processor) is provided either by the Adapter Board or routed through it from the Host. The voltage source selection (VMCU) is managed by the Power Mode Switch on the Adapter Board.

The available power modes are:

• BUF: An on-board voltage buffer senses the Host's voltage and replicates it, drawing current from the local 5V power net. The target device does not draw current from the Host power domain. This mode provides two analog outputs via a built-in current sense amplifier, proportional to the current drawn by the target device, allowing separate measurement of Host and Device power consumption. It is recommended for high-power applications where the Host voltage rail is insufficient. In this mode, the Energy Profiler tracks only the EFR32 device's current when an EFR32 acts as Host with a Radio Board.
• HOST: The on-board buffer is disengaged, directly connecting Host and Device power domains. This mode allows measuring the combined power consumption of Host and Device. For example, when an EFR32 acts as Host and a SiWx91x Device is used, the Energy Profiler tracks the current absorbed by both simultaneously.

The factory default mode is BUF. The Adapter Board supports Host operating voltages between 1.8V and 3.6V in both modes.

Figure 5.2: Adapter Board Power Topology. This diagram illustrates the power flow within the Adapter Board, showing connections from RPi HAT, Shield, EXP Header to the 5V POWER input, through the Hi-Z Input Voltage Buffer, HG/LG Current Sense Analog Outputs, and the Power Mode Switch to the VMCU and Radio Board Interface.

6. Current Measurements

Measuring co-processor current consumption is more complex than for microcontrollers. Co-processors typically require host instructions to enter specific states for testing, unlike microcontrollers which can be programmed for self-testing. Accurate measurements require connected communication ports and equal signal levels between Host and co-processor IO ports to prevent back-feeding. Dynamic back-feeding can occur during co-processor wake-up events, potentially going unnoticed in steady-state checks. Current meters with variable resistances have limited dynamic response and may cause back-feeding.

The methods described aim to ensure correct operation across power domains and prevent back-feeding. The choice of method depends on the measurement scope; the first is for fast transients, the second for accurate average values (e.g., battery lifetime estimation).

Before measuring, read Section 5 (Power Supply) to understand power modes and select the appropriate measurement method.

6.1 Analog Outputs

In BUF mode, the on-board voltage buffer supplies current to the co-processor, balancing Host and co-processor power domains. This circuit provides two uncalibrated, single-ended analog voltage outputs with different gains:

• LG (BO707): Low Gain Current Sense output with a gain factor of 1 A/V. A 30mV reading corresponds to 30 mA current¹.
• HG (BO705): High Gain Current Sense output with a gain factor of 101 A/V. A 30mV reading corresponds to 297 µA current¹.

An unamplified differential voltage output across a 0.5 Ω sense resistor is also provided (I_SNS +/-).

Suitable instruments for measuring single-ended voltage outputs include digital voltmeters and oscilloscopes with high impedance probes (1 MΩ - 10 MΩ). For differential voltage output, 10 MΩ probes are recommended.

• Digital Voltmeters or Multimeters are suitable for average current measurements. To prevent aliasing, ensure the averaging window is at least one order of magnitude larger than the longest period (cycle) implemented in firmware. A digital voltmeter can help estimate battery lifetime.
• Oscilloscopes offer lower resolution but can track dynamic current changes. Refer to Section Operating Characteristics for available bandwidths.

For breakout pad locations, refer to Section 4.6 Breakout Pads.

Zero-current voltage: This variable offset must be read and subtracted to calculate absolute current consumption. To read it, switch the power to HOST mode and measure the output voltage. Return to BUF mode for actual current readings.

For detailed specifications, refer to Section 2.2 Operating Characteristics.

Procedure summary for reading average currents with analog outputs:

1. Switch to HOST mode and read the Zero-current voltage.
2. Switch to BUF mode and read the current consumption, ensuring the averaging window is appropriate for application code events.
3. Subtract the Zero-current voltage (from step 1) from the current reading (step 2) to find the actual current consumption.

Note 1: Account for Zero-current voltage when measuring small currents (e.g., sleep currents). For currents over 50mA, the Zero-current voltage accounts for less than 1%.

6.2 Using External Current Meters

In HOST mode, the current drawn by the co-processor is tracked alongside the Host and other devices on the same power domains. Direct co-processor current measurement is not possible in this mode, but indirect measures can be derived. For example, using Studio's Energy Profiler, switch between HOST mode (total power consumption) and BUF mode (EFR32 power consumption). The difference estimates the average current. This method also applies to connecting external meters to auxiliary nodes on the Wireless Pro Kit (requires BAT mode and auxiliary power).

Figure 6.1: Example of current measurement set up with external meter. This diagram shows a typical setup for current measurement using an external meter, involving the WPK, Adapter Board, and external supply connections.

Procedure summary for reading average currents with external current monitoring tools:

1. Switch to HOST mode and read the total current consumption of Host + co-processor. Ensure the averaging window is appropriate for application code events.
2. Switch to BUF mode and read the current consumption of the Host alone.
3. Subtract the Host current (from step 1) from the current read in step 2 to estimate the average current consumption of the co-processor.

Note 2: The analog voltage outputs from the on-board voltage buffer provide no valid output in HOST mode and are only usable for reading the Zero-current voltage.

7. Downloading Firmware to SiWx91x Wi-Fi Co-processors

SiWx91x co-processors typically enter ISP mode after a reset. Follow these steps to download firmware using the on-board USB:

1. Connect the Adapter Board to a compatible host board.
2. Set the UART switch to USB mode.
3. Connect a USB cable to the Adapter Board's USB connector to activate the on-board USB-UART bridge (refer to Figure 6.1 for example).
4. Briefly press the RESET button.

Upon receiving a capital "U", the SiWx91x device will display the bootloader menu. The default Baud Rate is 115200 bps and can be changed within the bootloader menu.

Note that host applications might interfere with firmware upgrades by potentially pulling the reset line during flashing.

To download firmware from the Host to the Device over UART, the UART switch must be set to HOST. If SPI or SDIO interfaces are used, the UART switch setting is irrelevant. The RESET line is mapped across all host interfaces.

If no USB cable is connected, the USB bridge is deactivated to prevent undesired activity on the UART lines. The USB bridge is powered by the 5V rail and does not draw current from the Device power domain.

Note: The host's output pin controlling the co-processor's #DEV_RESET signal must be configured as open drain.

8. Schematics, Assembly Drawings, and BOM

Schematics, assembly drawings, and Bill of Materials (BOM) are available through Simplicity Studio after installing the kit documentation package. They are also accessible from the kit's page on the Silicon Labs website: silabs.com.

9. Kit Revision History

The kit revision is printed on the kit packaging label, as shown in the figure below. This section lists revisions; minor changes may be omitted.

Figure 9.1: Kit Label. An example of a kit label showing Part: SiWx917-EB4346x, Date: 31-10-23, S.nr: 1940000224, Qty: 1, and Rev.A00.

9.1 SiWx917-EB4346A Revision History

9.2 Si-EB8045A Revision History

9.3 Si-EB8045B Revision History

9.4 Si-EB8045C Revision History

10. Document Revision History

Revision 1.6

September 2024

• Kit ordering information updated. Prerequisite section added. Performance, Connector, and Downloading Firmware sections updated.

Revision 1.0

December 2023

• Initial document revision.