Silicon Laboratories EFM8 Series Operating instructions

AN954: Programming Guide for EFM8 and
EZRadio®
This document is intended to serve as a guide for application development with EZRa-
dio® Si4x55 ICs. It introduces the major parts of the hardware platform, such as the RF
Pico board, which contains the radio and the necessary RF components required to op-
erate the device according to a desired regulatory standard.
It introduces the energy friendly microcontroller 8-bit (EFM8) which is required to con-
trol the radio, evaluate the RF parameters, and develop custom application programs.
Besides the hardware, this document also describes the application programming inter-
face (API) that makes it possible for the EFM8 and RF Pico board to communicate with
each other. Using the software tools provided by Silicon Labs and following this pro-
gramming guide will make software development as easy as possible, as these items
will assist in configuring the radio effectively.
KEY POINTS
• EFM8 along with an EZRadio is an ultra-
low cost two-chip wireless solution.
• The EZRadio is a sub-GHz wireless
communcation platform that can be a
receiver, transmitter, or tranciever.
• Configuration of the EZRadio can be done
with a simple GUI within a free tool
provided by Silicon Labs.
• Configuration of peripherals and pinouts on
the EFM8 is performed using an intuitive
GUI.
silabs.com | Smart. Connected. Energy-friendly. Rev. 0.1

1. Hardware
This section will introduce the hardware needed for this reference design and demo. Using an EFM8 along with an EZRadio is a two
chip low cost wireless solution. This section will also discuss the connections between the radio, the MCU, and the expansion board
used to connect the two.
1.1 Kits
In order to run the software demos and get started with developing, 3 boards are required. EFM8BB1, Expansion Board, and Si4455
1.2 Busy Bee Starter Kit
The EFM8BB1 Starter Kit (STK) is a platform that allows the user to demonstrate, evaluate, and develop solutions. This kit includes the
EFM8BB1 8-bit MCU. It has vast functionality and utilizes an LCD, buttons, joystick, debug interface, and much more to allow rapid
evaluation of both the MCU itself and any add-on hardware using the expansion (EXP) header.
Kit USB
Connector
CR2032
Battery Holder
Power Source Select
User Push
Buttons User LED
EFM8 Reset Button
EFM8BB1 MCU
Expansion
Header
Direct
Debug Connector
Joystick
128x128 Pixel
Memory LCD
Debug IN/OUT
Connector
Reference
Board Connector
Figure 1.1. Busy Bee Starter Kit
AN954: Programming Guide for EFM8 and EZRadio ®
Hardware
silabs.com | Smart. Connected. Energy-friendly. Rev. 0.1 | 1

1.3 RF Pico Card
The RF pico board is a radio module that contains an EZRadio IC, a matching network, and an SMA connector on the top side. Other
than the antenna connector, these components are covered by a metal shield for noise reduction. The digital signals of the radio
(SCLK, SDI, SDO, NSEL, SCL, SDA, VDD and GND) can be accessed on test points at the edge of the board. The boards also have a
factory-loaded board identification memory (EBID) on the bottom side that contains data that describes the board properties. Via the
unified RF pico connector pair on the bottom side of the board, any RF Pico board can be connected to the EXP board explained next.
The Pico card comes with an antenna which is screwed into the SMA connector on the top of the card.
Antenna Connection
Noise Shield
Test Points
Figure 1.2. RF Pico Card
AN954: Programming Guide for EFM8 and EZRadio ®
Hardware
silabs.com | Smart. Connected. Energy-friendly. Rev. 0.1 | 2

1.4 Expansion Board
The expansion (EXP) board is used to connect the EFM8 Starter Kit to the RF Pico board. It has two sets of headers on each side, one
male, and one female. These are both mirrors of each other and can be used to transfer SPI, GPIOs, power, and ground. The RF Pico
card sits on top of this EXP board via the RFP1/2 ports located in the middle of the EXP board. A further layout of all the ports and
connections are outlined in the following figures and tables.
Female Expansion Header
(Connects to STK) Pico Card Connectors
Male Expansion Header
Figure 1.3. Expansion Board
1
3
5
7
9
11
13
15
17
19
GND
RF_NIRQ
RF_SDN
P1.5
P1.6
NC
P0.5
P1.3
EBID_SCL
EBID_SDA
VMCU
MOSI
MISO
SCLK
RF_NSEL
P0.4
P0.5
P1.2
5V
3V
Expansion Header Pins
2
4
6
8
10
12
14
16
18
20
Figure 1.4. Expansion Board 20-pin Header
AN954: Programming Guide for EFM8 and EZRadio ®
Hardware
silabs.com | Smart. Connected. Energy-friendly. Rev. 0.1 | 3

1
3
5
7
9
11
13
15
17
19
GND
NC
NC
NC
NC
NC
NC
SCL
3V3
GND
GND
NC
NC
NC
NC
NC
NC
SDA
3V3
GND
RFP2 Connector
2
4
6
8
10
12
14
16
18
20
1
3
5
7
9
11
13
15
17
19
GND
MOSI
SCLK
RF_NIRQ
SDA
RF_GPIO_0
RF_GPIO_2
NC
VRF
GND
GND
MISO
RF_NSEL
RF_SDN
SCL
RF_GPIO_1
RF_GPIO_3
NC
VRF
GND
RFP1 Connector
2
4
6
8
10
12
14
16
18
20
Figure 1.5. RFP1 and RPF2 Connectors
Table 1.1. EZRadio to EFM8 Connections
Pin Name Pin Function BB1 STK Pin
GND Ground GND
VDD Voltage Supply VDD
NIRQ Interrupt output, active low P0.0
SDN Shutdown input, active high P1.5
NSEL SPI select input P1.1
SCLK SPI clock P1.0
SDI SPI data input P0.6
SDO SPI data output P0.7
1.5 Radio Hardware Interface
The EZRadio devices can be controlled by the host MCU over a SPI bus and six additional signals. The user has access to the radio's
API via the SPI bus.
Table 1.2. SPI Signals
Signal Description
SCLK Serial clock, output from master
SDI Master output, slave input(MOSI)
SDO Master input, slave output(MISO)
NSEL Slave select, active low
The high state of the shutdown (SDN) pin is used to completely disable the radio and put the device into the lowest power consumption
state. The radio has an interrupt output pin (NIRQ) that can be used to promptly notify the host MCU of multiple events. The NIRQ pin is
active low and goes back to high if the pending interrupt flag is cleared by reading the appropriate interrupt pending registers.
AN954: Programming Guide for EFM8 and EZRadio ®
Hardware
silabs.com | Smart. Connected. Energy-friendly. Rev. 0.1 | 4

1.6 Setting Up the Hardware
1. Connect an RF Pico Board to the expansion board via the RFP1/2 connectors.
2. Connect the antenna to the SMA connector on the RF Pico Board.
3. Connect the BB1 starter kit to the expansion board via the 20 pin header.
4. Provide power to the board by connecting the DBG USB connector to the PC using the provided USB cable.
5. Move the switch to the AEM position.
6. Wait for Windows to install the driver of the debug interface, if necessary.
Figure 1.6. Setting up the BB1 STK
AN954: Programming Guide for EFM8 and EZRadio ®
Hardware
silabs.com | Smart. Connected. Energy-friendly. Rev. 0.1 | 5

2. Software
The first step to getting started with the EFM8BB1 is download Simplicty Studio from the Silicon Labs website (http://www.silabs.com/
simplicity-studio). Follow the installation wizard for a complete install. More information on specific tools included in Simplicity Studio
and their usage can be found at http://www.silabs.com/products/mcu/Pages/simplicity-studio.aspx.
The second software tool needed is Wireless Development Suite or WDS. This tool allows complete custimization to radio parameters.
It can be downloaded at https://www.silabs.com/products/wireless/EZRadio/Pages/WirelessDevelopmentSuite.aspx. For more informa-
tion on WDS please refer to AN796 found at http://www.silabs.com/Support%20Documents/TechnicalDocs/AN796.pdf.
2.1 Simplicity Studio
Simplicity Studio is a free tool offered by Silicon Labs that includes an IDE and many other tools to speed up development. This is the
main tool for developing on Silicon Labs' MCUs and running demos with the kit. Be sure that Simplicity Studio is installed and updated,
and the BB1 Starter Kit is connected. Once launched, Simplicity Studio will automatically detect any connected devices that it recogni-
zes. After connecting the BB1 kit, the device will appear in the [Detected Hardware] area of the main Simplicity Studio launcher.
Note: There may be a delay after connecting the kit before it appears in Simplicity Studio. If the kit does not appear, ensure the switch
is in the AEM position and that the J-Link drivers are installed.
Figure 2.1. Simplicity Studio Main Page
2.2 Wireless Development Suite
Silicon Labs provides a powerful tool to help with EZRadio/PRO software development, the Wireless Development Suite (WDS). It is
available at https://www.silabs.com/products/wireless/EZRadio/Pages/WirelessDevelopmentSuite.aspx. WDS allows the user to virtual-
ly select a radio and use the EZConfigPRO Setup GUI. This setup interface provides an easy path to quickly select and load the de-
sired configuration for the EZRadio/PRO devices. The EZConfigPRO Setup allows four different methods for device setup.
AN954: Programming Guide for EFM8 and EZRadio ®
Software
silabs.com | Smart. Connected. Energy-friendly. Rev. 0.1 | 6

After the desired configuration is selected, the program gives the option to generate a header file which will contain all of the options
selected in the GUI. This file can then be used in a Simplicity Studio project to configure the radio and communicate with an MCU.
Using the header file generated by the WDS is highly recommended. Manual editing in the header file may cause problems and prevent
the radio from working correctly. For more complete information on WDS and EZConfigPRO usage, refer to the WDS User's Guide.
The following figures will be a guide to generating a customized header file. The reference design provided by Silicon Labs has a con-
figuration file already included in the project. However, to make changes to the radio configurations it is recommended to generate a
new one.
Note: WDS is not necessary for getting the software demos running; however WDS is needed to customize the radio configuration.
Figure 2.2. WDS Introduction
WDS can be used without connecting the physical HW to the PC to obtain configuration parameters. After running the WDS, the user
needs to start simulation mode by clicking on the [Simulate radio button.]
Figure 2.3. WDS Simulate Device
AN954: Programming Guide for EFM8 and EZRadio ®
Software
silabs.com | Smart. Connected. Energy-friendly. Rev. 0.1 | 7

Figure 2.4. WDS Device Selection
Once the Radio is selected, the radio configurations screen will appear. This is the main page used to generate a configuration file that
can be used in a custom project. Preset configurations like Standard Packet TX and Unmodulated Carrier are available to quickly set up
a radio project. The Empty Framework project can be used as a blank template. Once the configurations are set, the [Generate
Source] button can be used to create the header file.
Note: WDS does not support EFM8 products. There are options to generate an entire project with MCU source code, however these
projects and code will most likely not work on EFM8 MCUs. When working with EFM8 and EZRadio/PRO, WDS is only used to gener-
ate the header file.
AN954: Programming Guide for EFM8 and EZRadio ®
Software
silabs.com | Smart. Connected. Energy-friendly. Rev. 0.1 | 8

Figure 2.5. WDS Configuration
The generated header file can be used in a new or existing project within Simplicity Studio, or used with any other IDE.
AN954: Programming Guide for EFM8 and EZRadio ®
Software
silabs.com | Smart. Connected. Energy-friendly. Rev. 0.1 | 9

3. Software Demos
This document covers two demos, which run on combination of EFM8BB1 and a Si4455. The Range Test is used to evaluate the two-
chip solution of an EZRadio and an EFM8. The Bidirectional demo is used as a development platform.
The radio_config.h file holds the radio configurations and is a great learning tool for understanding how the radio is set up. The radio
API is located in the radio.c/h files. These functions are used to communicate to the radio and they will be further explained later in
this document.
3.1 Range Test
The Range test demo is an evaluation tool that allows the user to evaluate the combination of EFM8 and a sub-GHz radio. It has config-
urable settings that the user can alter and measure to know how this combination will perform in a specific application.
The menu screen of the demo has the user set a few parameters before entering into transmit mode or receive mode. The first configu-
rable parameter is the self identification (ID) and destination ID. These are used to communicate with specific boards. To send a packet
between two kits the destination ID of the transmitter and self ID of the receiver must match and the self ID of the transmitter must
match the destination ID of the receiver. North and south on the joystick set the ID, and center of the joystick specifies which ID is being
altered.
The packet size is fixed at a size of seven but the number of packets to send can be altered. Once all of the parameters are set to the
desired values, the west and east positions of the joystick can be used to set the demo into transmit or receive mode.
In transmit mode, the screen will indicate the ID of the board, the ID to be sent to, the max number of packets to be sent, and the
number that has been sent. West on the joystick can be used to go back to the menu screen and change parameters. Center on the
joystick controls the transmission of packets. Pushing it begins the transmission which will continue until the max number of packets
has been sent. Center again can be used to stop and reset the number of packets sent.
In receive mode, the screen will show the IDs, percent of packets correctly received (PER), receive sensitivity (RSSI), number of pack-
ets received, and number of packets sent. When a packet is received the packets received, packets sent, RSSI, and PER will update.
Again, west can be used to go back to the menu screen.
Figure 3.1. Range Test Menu, Transmit, and Receive Screens
3.2 Bidirectional Packet
The Bidirectional Packet demo is a simple example of the Si4455 wireless radios along with an EFM8 BB1 starter kit. It is controlled via
the two push buttons on the starter kits. The tri-colored LED indicates either a button press or when a packet is received.. At first, the
LED is green and the push buttons cycle through the colors and transmit the state. The receiver will match the state of the sender such
that the two boards, when configured correctly and within range, will have the same color LEDs illuminated. The packet is 7 bytes, and
the last byte indicates the state of the transmitting board. This project is intended to be a starting point for developing an application
utilizing the sub-GHz radio and an EFM8 MCU.
3.3 Running the Demos
To get the software demos running, follow the steps for installing Simplicity Studio, putting the kit together, and connecting the kit to the
host or PC as shown in the figure.
AN954: Programming Guide for EFM8 and EZRadio ®
Software Demos
silabs.com | Smart. Connected. Energy-friendly. Rev. 0.1 | 10

2. Insert the EXP board onto
the STK via 20 pin header
1. Inset the RF Pico card
onto the EXP board
3. Flip the switch to AEM
4. Connect the USB cable
from the STK to the host PC
Figure 3.2. Assembling the Kit
With Simplicity Studio launched and the BB1 kit recognized, select [Software Demos]. Navigate to find the [Wireless] folder and
choose a demo. Select the Range Test demo by selecting the [EFM8BB1_Range_Test_Si4455]. Once the demo is deployed the menu
screen should appear on the starter kit.
AN954: Programming Guide for EFM8 and EZRadio ®
Software Demos
silabs.com | Smart. Connected. Energy-friendly. Rev. 0.1 | 11

Figure 3.3. Example Project Tree — Range Test
Some of the important files within the demo are described below.
File Name: main.c
Description: Contains all the logic for the demo, state controls, and API calls to the radio. Contains the screen outputs.
File Name: master_bsp.h
Description: Serves as glue for the entire project. It links all the libraries and files needed for the radio, SPI, screen, etcFile Name: Ini
tDevice.c
AN954: Programming Guide for EFM8 and EZRadio ®
Software Demos
silabs.com | Smart. Connected. Energy-friendly. Rev. 0.1 | 12

Description: Contains hardware configurations of the 8-bit MCU including pin states, clocks, interrupts, SPI configuration, and more.
File Name: radio.c/h
Description: Contains the API functions, defines, and variables for the EZRadio. These functions add an abstraction layer for the user
and allow higher level calls. Some of the functions are explained later in this document.
File Name: radio_config.h
Description: Contains all of the configurations for the radio. The radio properties are set here, including frequency, packet size, data
rate, modulation, etc., as well as the GPIO configuration.
With the demo up and running the next part of this document will begin to go into detail about the radio. Understanding the radio in
depth will better enable customization for building a specific radio application.
AN954: Programming Guide for EFM8 and EZRadio ®
Software Demos
silabs.com | Smart. Connected. Energy-friendly. Rev. 0.1 | 13

4. Application Programming Interface
The programming interface allows the user to do the following:
• Send commands to the radio.
• Read status information.
• Set and read radio parameters.
• Handle the transmit and receive FIFOs.
The API commands are listed in the table below. The following sections describe the SPI transactions of sending commands and get-
ting information from the chip.
Table 4.1. EZRadio/Pro API Commands
Command ID Name Description
BOOT_COMMANDS
0x02 POWER_UP Command to power-up the device and se-
lect the operational mode and functionality.
COMMON_COMMANDS
0x00 NOP No operation command.
0x01 PART_INFO Reports basic information about the device.
0x10 FUNC_INFO Returns the Function revision information
of the device.
0x11 SET_PROPERTY Sets the value of one or more properties.
0x12 GET_PROPERTY Retrieves the value of one or more proper-
ties.
0x13 GPIO_PIN_CFG Configures the GPIO pins.
0x15 FIFO_INFO
Access the current byte counts in the TX
and RX FIFOs and pro- vide for resetting
the FIFOs.
0x20 GET_INT_STATUS
Returns the interrupt status of ALL the pos-
sible interrupt events (both STATUS and
PENDING). Optionally, it may be used to
clear latched (PENDING) interrupt events.
0x33 REQUEST_DEVICE_STATE Request current device state and channel.
0x34 CHANGE_STATE Manually switch the chip to a desired oper-
ating state.
0x38 OFFLINE_RECAL Recalibrates due to temperature change.
0x44 READ_CMD_BUFF Used to read CTS and the command re-
sponse.
0x50 FRR_A_READ Reads the fast response registers (FRR)
starting with FRR_A.
0x51 FRR_B_READ Reads the fast response registers (FRR)
starting with FRR_B.
0x53 FRR_C_READ Reads the fast response registers (FRR)
starting with FRR_C.
0x57 FRR_D_READ Reads the fast response registers (FRR)
starting with FRR_D.
IR_CAL_COMMANDS
0x17 IRCAL Image rejection calibration.
AN954: Programming Guide for EFM8 and EZRadio ®
Application Programming Interface
silabs.com | Smart. Connected. Energy-friendly. Rev. 0.1 | 14

Command ID Name Description
0x19 IRCAL_MANUAL Image rejection calibration.
TX_COMMANDS
0x31 START_TX Switches to TX state and starts transmis-
sion of a packet.
0x37 TX_HOP Hop to a new frequency while in TX.
0x66 WRITE_TX_FIFO Writes data byte(s) to the TX FIFO.
RX_COMMANDS
0x16 PACKET_INFO
Returns information about the length of the
variable field in the last packet received
and (optionally) overrides field length.
0x22 GET_MODEM_STATUS
Returns the interrupt status of the Modem
Interrupt Group (both STATUS and PEND-
ING). Optionally, it may be used to clear
latched (PENDING) interrupt events.
0x32 START_RX Switches to RX state and starts reception
of a packet.
0x36 RX_HOP Manually hop to a new frequency while in
RX mode.
0x77 READ_RX_INFO Reads data byte(s) from the RX FIFO.
ADVANCED_COMMANDS
0x14 GET_ADC_READING
Performs conversions using the Auxiliary
ADC and returns the results of those con-
versions.
0x21 GET_PH_STATUS
Returns the interrupt status of the Packet
Handler Interrupt Group (both STATUS and
PENDING). Optionally, it may be used to
clear latched (PENDING) interrupt events.
0x23 GET_CHIP_STATUS
Returns the interrupt status of the Chip In-
terrupt Group (both STATUS and PEND-
ING). Optionally, it may be used to clear
latched (PENDING) interrupt events.
4.1 API Functions
The provided software examples heavily utilizes the radio API to communicate and successfully transmit packets. Some of the impor-
tant API functions are defined and elaborated on below.
Function Name: void si4455_reset(void)
Description: This function is used to reset the Si446x radio by applying shutdown and releasing it. After this function si4455_boot
should be called. You can check if power-on reset has completed by waiting 4ms or by polling GPIO0, 2, or 3. When these GPIOs are
high, it is safe to call si4455_boot.
Return Value: None
Function Name: void si4455_power_up(U8 BOOT_OPTIONS, U8 XTAL_OPTIONS, U32 XO_FREQ)
Description: This function is used to initialize the radio after power-up.
Input Parameter(s): BOOT_OPTIONS: Patch mode selector.
XTAL_OPTIONS: Select if TCXO is in use.
XO_FREQ: Frequency of TCXO or external crystal oscillator in Hz.
AN954: Programming Guide for EFM8 and EZRadio ®
Application Programming Interface
silabs.com | Smart. Connected. Energy-friendly. Rev. 0.1 | 15

Return Value: None
Note: Before this function si4455_reset should be called.
Function Name: U8 si4455_configuration_init(const U8*pSetPropCmd)
Description: This function is used to load all properties with a list of NULL terminated set property commands.
Input Parameter(s): *pSetPropCmd: First element of the list to be loaded.
Return Value: SI4455_COMMAND_ERROR: the list of commands is wrong.
SI4455_CTS_TIMEOUT: If a CTS error occurs.
SI4455_SUCCESS: If loading is successful.
Note: Before this function si4455_reset should be called.
Function Name: void si4455_start_tx(U8 CHANNEL, U8 CONDITION, U16 TX_LEN)
Description: Sends START_TX command to the radio.
Input Parameter(s): CHANNEL: Channel number.
CONDITION: Start TX condition.
TX_LEN: Payload length (exclude the PH generated CRC).
Return Value: None
Function Name: void si4455_start_rx(U8 CHANNEL, U8 CONDITION, U16 RX_LEN, U8 NEX- T_STATE1, U8 NEXT_STATE2, U8
NEXT_STATE3)
Description: Sends START_RX command to the radio.
Input Parameter(s): CHANNEL: Channel number.
CONDITION: Start RX condition.
RX_LEN: Payload length (exclude the PH generated CRC).
NEXT_STATE1: Next state when Preamble Timeout occurs.
NEXT_STATE2: Next state when a valid packet received.
NEXT_STATE3: Next state when invalid packet received (e.g., CRC error).
Return Value: None
Function Name: void si4455_get_int_status(U8 PH_CLR_PEND,U8 MODEM_CLR_PEND, U8 CHIP_CLR_PEND)
Description: Get the Interrupt status/pending flags form the radio and clear flags if requested.
Input Parameter(s): PH_CLR_PEND: Packet Handler pending flags clear.
MODEM_CLR_PEND: Modem Status pending flags clear.
CHIP_CLR_PEND: Chip State pending flags clear.
Return Value: None
Function Name: void si4455_write_tx_fifo(U8 numBytes, U8* pTxData)
Description: The function can be used to load data into TX FIFO.
Input Parameter(s): numBytes: Data length to beload.
pTxData: Pointer to the data (U8*).
AN954: Programming Guide for EFM8 and EZRadio ®
Application Programming Interface
silabs.com | Smart. Connected. Energy-friendly. Rev. 0.1 | 16

Return Value: None
Function Name: void si4455_read_rx_fifo(U8 numBytes, U8* pRxData)
Description: Reads the RX FIFO content from the radio.
Input Parameter(s): numBytes: Data length to be read.
pRxData: Pointer to the buffer location.
Return Value: None
Function Name: void si4455_frr_d_read(U8 respByteCount)
Description: Reads the Fast Response Registers starting with D register into Si4455Cmd union.
Input Parameter(s): respByteCount: Number of Fast Response Registers to be read.
Return Value: None
4.2 Sending Commands to the Radio
The behavior of the radio can be changed by sending API commands to the radio. The radio can be configured through several proper-
ties that hold radio configuration settings, such as interrupt settings, modem parameters, packet handler settings, etc. For most of the
commands, the host MCU does not expect any response from the radio chip. Instead, other commands are used to read back a proper-
ty from the chip, such as checking the interrupt status flags, reading the transmit/receive FIFOs.
The radio processes the request after receiving a command. During this time, the radio is not capable of receiving a new command.
The host MCU has to poll the radio and identify when the next command can be sent. The clear to send (CTS) signal shows the actual
status of the command buffer of the radio. It can be monitored over the SPI or on GPIOs, or the chip can generate an interrupt if it is
ready to receive the next command.
4.3 Checking that the Radio is Ready
4.3.1 Software Polling Method
To ensure the radio is ready to receive the next command, the host MCU has to pull down the select (NSEL) pin to monitor the status of
clear to send (CTS) over the SPI port. The 0x44 command ID has to be sent and eight clock pulses have to be generated on the SCLK
pin. During the additional eight clock cycles, the radio clocks out the CTS as a byte on the SDO pin. When completed, NSEL should be
pulled back to high. If the CTS byte is 0xFF, it means that the radio processed the last command successfully and is ready to receive
the next command; in any other case, the CTS read procedure has to be repeated from the beginning as long as the CTS byte is not
0xFF.
Figure 4.1. Software Polling
4.3.2 GPIO Checking Method
Any GPIO can be configured for monitoring CTS. GPIOs can be configured to go either high or low when the chip has completed the
command. The function of the GPIOs can be changed by the GPIO_PIN_CFG command. By default, GPIO1 is set as "High when com-
mand completed, low otherwise" after power-on reset. Therefore, this pin can be used for monitoring CTS right after power-on reset to
know when the chip is ready to boot up.
AN954: Programming Guide for EFM8 and EZRadio ®
Application Programming Interface
silabs.com | Smart. Connected. Energy-friendly. Rev. 0.1 | 17

4.3.3 NIRQ Interrupt Checking Method
The radio asserts the CHIP_READY interrupt flag if a command is completed. The interrupt flag can be monitored by either the
GET_CHIP_STATUS or the GET_INT_STATUS command. Apart from monitoring the interrupt flags, the radio may pull down the NIRQ
pin if this feature is enabled. If a new command is sent while the CTS is asserted, then the radio ignores the new command. The radio
can generate an interrupt to communicate this error to the MCU by the CMD_ERROR interrupt flag in the CHIP_STATUS group. The
interrupt flag has to be read (by issuing a GET_CHIP_STATUS or GET_INTERRUPT_STATUS command) to clear the pending inter-
rupt and release the NIRQ pin. No other action is needed to reset the command buffer of the radio, but, after a CMD_ERROR, the host
MCU should repeat the new command after the radio has processed the previous one.
All the commands that are sent to the radio have the same structure. After pulling down the NSEL pin of the radio, the command ID
should be sent first. The commands may have up to 15 input parameters.
Figure 4.2. NIRQ Method
4.4 Getting Response from the Radio
Reading from the radio requires several steps to be followed. The host MCU should send a command with the address it requests to
read. The radio holds the CTS at a non-0xFF value while it retrieves the requested information. Once the CTS is set (0xFF), the host
MCU can read the answer from the radio.
Send
Command Read CTS Retrieve
Response
CTS Value 0xFF
Not
0xFF
Figure 4.3. Read Procedure
If CTS is polled on the GPIOs, or the radio is configured to provide an interrupt if the answer is available, then the response can be read
out from the radio with the following SPI transaction.
AN954: Programming Guide for EFM8 and EZRadio ®
Application Programming Interface
silabs.com | Smart. Connected. Energy-friendly. Rev. 0.1 | 18

Figure 4.4. Read Response From Radio
If CTS is polled over the SPI bus, first the host MCU should pull the NSEL pin low. This action should be followed by sending out the
0x44 Read command ID and providing an additional eight clock pulses on the SCLK pin. The radio will provide the CTS byte on its SDO
pin during the additional clock pulses. If the CTS byte is 0x00, then the response is not yet ready and the host MCU should pull up the
NSEL pin and repeat the procedure from the beginning until CTS becomes 0xFF. If CTS is 0xFF, then the host MCU should keep the
NSEL pin low and provide clock cycles on the SCLK pin, as many as the data to be read out requires. The radio will clock out the
requested data on its SDO pin during the additional clock pulses.
Figure 4.5. Monitor CTS and Read the Response
Reading the response from the radio can be interrupted earlier. For example, if the host MCU asked for five bytes of response, it may
read fewer bytes in one SPI transaction. As long as a new command is sent, the radio keeps the response for the last request in the
command buffer. The host MCU can read the response several times in a new SPI transaction. In such a case, the response is always
provided from the first byte.
Notes:
• Up to 16 bytes of response can be read from the radio in one SPI transaction. If more bytes are read, the radio will provide the same
16 bytes of response in a circular manner.
• If the command says that the host MCU expects N bytes of response, but during the read sequence, the host MCU provides less
than N bytes of clock pulses, it causes no issue for the radio. The response buffer is reset if a new command is issued.
• If the command says that the host MCU expects N bytes of response, but during the read sequence, the host MCU provides more
than N bytes of clock pulses, the radio will provide unpredictable bytes after the first N bytes. The host MCU does not need to reset
the SPI interface; it happens automatically if NSEL is pulled low before the next command is sent.
AN954: Programming Guide for EFM8 and EZRadio ®
Application Programming Interface
silabs.com | Smart. Connected. Energy-friendly. Rev. 0.1 | 19