ST SPWF04S Series User manual

Introduction
The SPWF04Sx series of Wi-Fi modules integrate a complete TCP/IP protocol stack and a rich set of applications including, but
not limited to, web server, web client RESTful API, TFTP, MQTT and SMTP.
Security is added in the multiple layers of Wi-Fi and peer-to-peer protocols. The stack implements the WPS protocol, WPA2 in
both the Personal and Enterprise options, and the TLS for end-to-end secure transactions.
Users access the features of the SPWF04Sx modules via UART using the simple AT command syntax, or via SPI using a
custom packet format and protocol.
To enable a complete customization of the application on the module, the SPWF04Sx software integrates a MicroPython
interpreter that provides the user with MicroPython standard libraries and a customized set of classes to export the specific
SPWF04Sx features.
The diagram below summarizes the possible integrations of an SPWF04Sx module in a target application.
Figure 1. SPWF04Sx user integration modes
This user manual is intended as a guide to the set of commands available on the UART or the SPI console. A description and
explanation of the configuration variables, status variables and asynchronous indication messages is available in the Appendix
of the manual.
This manual is not intended as a technical guide of Wi-Fi and TCP/IP, or other technologies available in the module.
TCP/IP protocol stack for SPWF04Sx Wi-Fi modules
UM2114
User manual
UM2114 - Rev 3 - November 2018
For further information contact your local STMicroelectronics sales office.
www.st.com

1SPWF04Sx software architecture description
The complete SW architecture of SPWF04S is shown in the diagram below.
Figure 2. SPWF04Sx software architecture
A block diagram of the SPWF04Sx protocol stack is provided in Figure 3. SPWF04Sx protocol stack diagram.
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Figure 3. SPWF04Sx protocol stack diagram
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2Interface and message types
As shown in Figure 1. SPWF04Sx user integration modes, the SPWF04Sx enables three options for integration of
the device in the final user application. Refer to the SPWF04Sx datasheet for information useful for
implementation, such as the pinout. The configuration variable, “console_enabled”, is used to define the module
interface to use.
•UART interface
“console_enabled=1”
The UART console provides a user-friendly interface built on a set of AT commands that allow an external
microcontroller connected to the SPWF04Sx UART to access the functions integrated in SPWF04Sx device.
UART is set as the module's default interface.
•SPI interface
“console_enabled=0”
The device can be connected as a slave to the SPI interface of an external microcontroller. An ad hoc SPI
protocol and corresponding packet format are defined.
•MicroPython scripting
"console_enabled=2” - to use Python together with AT commands over UART.
"console_enabled=3” - to use MicroPython only.
The device implements a scripting methodology based on an integrated MicroPython interpreter.
MicroPython scripts can map a target application, making it unnecessary to integrate the device with an
external processor.
The following four message types represent the type of data exchanged over the interfaces.
•Commands
Used to activate a feature defined within the stack. The list of commands supported is specified in
Table 1. SPWF04Sx commands.
•Command return messages
Synchronous messages that report the status of the execution of a command. The list of synchronous error
codes is reported in Section 8 in the Appendix.
•WINDs
Asynchronous messages reporting a network or radio status at the application level. The list of WIND
messages is reported in Section 8 in the Appendix.
•Data
Data sent to, or received (data payload) from, a remote device.
Table 1. SPWF04Sx commands
Command ID AT command Description
Utils: commands for debugging and retrieving module status
0x01 AT Null command
0x02 AT+S.HELP Help command
0x05 AT+S.STS Status configuration
0x35 AT+S.PEERS Peers configuration
Management: commands for module management and configuration
0x03 AT+S.RESET SW reset
0x04 AT+S.PMS Set power mode
0x08 AT+S.PYTHON Enter MicroPython execution
0x09 AT+S.GCFG Read Configuration status
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Command ID AT command Description
0x0A AT+S.SCFG Set configuration variables
0x0B AT+S.WCFG Save configuration to Flash
0x0C AT+S.FCFG Restore factory configuration
0x57 AT+S.FSWRITE FS update via serial UART/SPI
0x58 AT+S.FSUPDATE FS download
0x56 AT+S.FWUPDATE FW download
STM32 peripherals: commands to manage the peripherals and related values
0x13 AT+S.GPIOC Configure GPIO
0x14 AT+S.GPIOR Read GPIO
0x15 AT+S.GPIOW Write GPIO
0x16 AT+S.DAC Disable/Enable DAC
0x17 AT+S.ADC Read ADC value
0x18 AT+S.PWM Set PWM
0x11 AT+S.TIME Get/Set time
0x12 AT+S.RANDOM Provide random number
File system management
0x21 AT+S.FSM Mount volume
0x22 AT+S.FSU Umount/Erase volume
0x23 AT+S.FSC Create file, append data
0x25 AT+S.FSD Delete file
0x26 AT+S.FSR Rename file
0x27 AT+S.FSL List existing files
0x28 AT+S.FSP Print file content
0x29 AT+S.HASH Compute digest
Security: commands to interact with the security features
0x2A AT+S.WPAECERT Manage WPA-Enterprise certificates
0x2B AT+S.TLSCERT Manage TLS certificates
0x36 AT+S.WPS Initiate a WPS Exchange
Radio: commands to manage main Wi-Fi operations
0x32 AT+S.WIFI Set Wi-Fi radio
0x33 AT+S.SCAN Network scan
0x34 AT+S.SSIDTXT Get/Set ASCII SSID
0x39 AT+S.PING Ping a specified host
Sockets: commands to manage socket read and write
0x41 AT+S.SOCKON Open a socket client
0x42 AT+S.SOCKQ Query a socket client for pending data
0x43 AT+S.SOCKC Close a socket client
0x44 AT+S.SOCKW Write data to a socket server
0x45 AT+S.SOCKR Read data from a socket client
0x46 AT+S.SOCKL List opened socket clients
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Command ID AT command Description
0x47 AT+S.SOCKDON Open a socket server
0x48 AT+S.SOCKDQ Query socket server for pending data
0x49 AT+S.SOCKDC Close a socket server
0x4A AT+S.SOCKDW Write data to a socket server
0x4B AT+S.SOCKDR Read data from a socket server
0x4C AT+S.SOCKDL List bound socket clients
Web sockets
0x61 AT+S.WSOCKON Open a web socket client
0x62 AT+S.WSOCKQ Query a web socket client for pending data
0x63 AT+S.WSOCKC Close web socket client
0x64 AT+S.WSOCKW Write data to a web socket client
0x65 AT+S.WSOCKR Read data from web socket client
0x66 AT+S.WSOCKL List open web socket client
Trivial FTP
0x51 AT+S.TFTPGET Get request to a TFTP server
0x52 AT+S.TFTPPUT Put request to a TFTP server
SMTP
0x53 AT+S.SMTP Send an email
HTTP
0x54 AT+S.HTTPGET Get a request to an HTTP server
0x55 AT+S.HTTPPOST Post request to an HTTP server
0x59 AT+S.INPUTSSI Fill buffer for raw text input SSI
MQTT
0x5A AT+S.MQTTCONN MQTT connect
0x5B AT+S.MQTTSUB MQTT subscribe
0x5C AT+S.MQTTPUB MQTT publish
0x5D AT+S.MQTTUNSUB MQTT unsubscribe
0x5E AT+S.MQTTDISC MQTT disconnect
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3AT commands over the UART
The factory module configuration sets the UART console mode as the default interface for the SPWF04Sx. This
corresponds to the configuration variable “console_enabled” being set to 1.
AT commands over the UART have a max length of 512 bytes; they are case insensitive and are always in the
form of:
AT+S. <cmd-parameters><cr>[data]
Note: Any command requiring data after the <cr> is not reentrant. If bytes are lost during data transfer over the
UART, the module remains in the waiting stage for incoming bytes.
A command is followed by a variable number of response lines that have the following format:
AT-S. <response-string><optional-parameters>
The AT command line, up to the terminating <cr>, is sent from the host. Response lines are sent from the module
to the host.
AT-S.OK:<free_heap>:<wifi_state>
returned when a command is successfully executed.
Note that free_heap and wifi_state are shown depending on
the "console_verbose" configuration variable value (0 to 2).
AT-S.ERROR:<error-code>:<error-string>
qualifies a synchronous error. The <error-code> field of each
asynchronous indication type is unique. The descriptive string
may be safely ignored.
Note that error_code and error_string are shown depending
on the "console_errs" configuration variable value (0 to 2).
Command parameters
A command can require parameters that follow an “=” character. The parameters are positional and separated by
a configurable separator (by default, a comma).
Parameters can require mandatory or optional values. In the latter case, if the value is not specified a default
value will be used. In the format of the command, an optional parameter is represented in squared brackets.
Asynchronous indications
Asynchronous indications may arrive at any time (except as noted below), and have the format:
+WIND:<number>:<descriptive-string>[:<variables>]<cr><lf>
The <number> field of each asynchronous indication type is unique. The descriptive string may be safely ignored.
Note that number and descriptive strings are shown depending on the "console_winds" configuration variable
value (0 to 2).
Refer to Section 8 in the Appendix for a complete list of WIND messages.
Note: Immediately after reset, no commands should be sent and only asynchronous indications are present until
the indication “+WIND:0:Console active<cr><lf>” is received. After this event, AT commands may be safely sent to
the device.
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4SPI protocol
By setting to 0 the configuration variable "console_enabled", the module is enabled to use the SPI interface in
place of the UART.
The data transferred over the MISO and MOSI signals are packed using a well-defined API packet format as
represented below.
Figure 4. SPI packet formats
Table 2. KindOfEvent Byte SubField
Bits Event type
Bits 0:3 Status variable wifi_state values range. Refer to
Table 8. Status variables.
Bits 4:7
Allowed values are:
• 0x01 for common indications like WIND or action
confirmations
• 0x02 for critical error notifications
• 0x03 for incoming data sent over the SPI (in this case
normally data are filled into payload field)
Table 3. Indication number field
Event type Bits 4:7 Indication number
0x01 Refer to Table 14. WIND messages.
0x02 Refer to Table 10. AT-S.ERROR:=ERROR ID= =ERROR
String=.
0x03 Data payload.
Commands over the SPI have a max length of 512 bytes.
To map an AT command in the equivalent SPI command, the following procedure applies:
1. Use the corresponding CMD ID specified in Table 1. SPWF04Sx commands and fill the 4th bytes of the
master packet.
2. If optional parameters are available, count the number of comma-separated items after the “=” character and
with that number the 6th byte of the message. Starting from the 7th byte, start to write 1 byte containing the
field lengths and then copy the field bytes. Then continue with the remaining parameters.
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3. Once the full payload has been filled, calculate the full message payload lengths and accordingly fill bytes 1
and 2 in the SPI message packet request.
First example
AT command: AT+S.FSL
1. Command ID: 0x25
2. Number of parameters: 0x00
3. Full message payload length: 0x02
Result: SPI message 0x02 0x00 0x02 0x25 0x00
Second example
AT command: AT+S.SCAN=d,/scan.txt
1. Command ID: 0x33
2. Number of parameters: 0x02
a. First Parameter: 0x01,d
b. Second Parameter: 0x09,"/scan.txt"
3. Full message payload length: 0x0D
Result: SPI Message 0x02 0x00 0x0D 0x33 0x02 0x01 d 0x09 "/scan.txt"
Third example
AT command: AT+S.SOCKW=0,5<Cr>hello
1. Command ID: 0x44
2. Number of parameters: 0x02
a. First Parameter: 0x01,0
b. Second Parameter: 0x01,5
3. Payload: "hello"
Result: SPI Message 0x02 0x00 0x0B 0x44 0x02 0x01 0 0x01 5 "hello"
Fourth example
Asynchronous event: +WIND:1:Poweron:170726-b7ac1ba-SPWF04S
1. kind of event (4bits): 0x01
2. wifi_state (4 bits): 0x0
3. Indication number: 0x01
4. Full message payload length: 0x16
Result: SPI Message 0x02 0x10 0x01 0x16 0x00 (170726-b7ac1ba-SPWF04S)
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5MicroPython scripting
The SPWF04Sx supports the MicroPython modes represented in Figure 5. MicroPython modes. The configuration
variable “console_enabled” identifies the use of the console together with MicroPython. In detail:
• "console_enabled" set to 2: this setting allows using both AT commands over the UART and MicroPython
REPL shell.
• "console_enabled" set to 3: this setting allows only a MicroPython preloaded script to be executed. No
UART/SPI communication is allowed to/from a host processor.
Consequently, the following Python modes are defined:
•Python Interactive Console (REPL – Read Evaluation Print Loop). Mainly used for debugging purposes,
it is activated by the AT+S.Python (Python command) launched without parameters. The REPL is exited by
using a CTRL-D escape character.
•Run Time Script execution. Activated with the Python command, it allows to execute the script specified as
parameter. After script execution, control returns to the AT console.
•DefaultScript Hard Execution. By using the GPIO(8) set to high at boot time, or when "console_enabled" is
set to 3, the module automatically enters the execution of the script specified by the variable “python_script”.
This mode allows the use of the module without a connected host. Note that "console_enabled" is not
changed by GPIO(8) access: this means that on the subsequent reboot, accessing Python mode again will
require GPIO(8) to be high.
Figure 5. MicroPython modes
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6Command reference guide
This section details each of the SPWF04Sx commands listed in Table 1. SPWF04Sx commands, including a brief
description of its behavior and complete list of parameters. Examples and syntax are described in the “AT” format
introduced in Section 3 AT commands over the UART. The mapping mechanism described in Section 4 SPI
protocol is used to map the AT command in the packet format used by the SPI.
6.1 AT
AT, by itself, is a null command that always returns an OK result code. It is useful for testing the module interface
for readiness.
Usage:
AT<cr>
Parameters:
None
6.2 AT+S.HELP
AT+S.HELP prints the list of all the AT commands supported with a brief help text for each of them. Refer to
Table 1. SPWF04Sx commands for a complete list of the commands available.
Usage:
1) AT+S.HELP<cr> to get the full list of commands
2) AT+S.HELP=<keyword><cr> to get the list of commands containing the specified keyword
Parameters:
<keyword> Specifies the name of a keyword
Result:
AT-S.Command:<command> -- <help>
<command> Specifies the command
<help> Specifies the description of the command
6.3 AT+S.STS
AT+S.STS displays the current values of all the status variables.
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Usage:
1) AT+S.STS<cr> to get the full list of configuration variables
2) AT+S.STS=<variable><cr> to get the value of the specified variable
Parameters:
<variable> Specifies the name of a variable. See Table 8. Status
variables for a list of the available status variables
Result:
AT-S.Var:<var>=<value>
<var> Specifies the status variable name
<value> Specifies the status variable value
6.4 AT+S.PEERS
AT+S.PEERS displays the current values of the peer table. These values are useful to obtain additional
information about the module connected to the AP or about the client connected to the module when it is
configured in Mini AP mode.
Usage:
1) AT+S.PEERS<cr> returns the list of peers variable
2) AT+S.PEERS=<peer_number><cr> returns the list of peers variable for the peer_number peer
3) AT+S.PEERS=<peer_number>,<peer_var><cr> returns the specific value of a peer_variable
Parameters:
<peer_number> identifier of the peer
<peer_var>
displays the current value of the specified peer variable. Refer
to Table 9. Peer variables in the Appendix for a complete list
of the peer variables
Result:
AT-S.Var:<id>.<var>=<value>
<id> Specifies the peer number
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<var> Specifies the peer variable name
<value> Specifies the peer variable value
6.5 AT+S.RESET
Command used to provide a SW reset to the module.
Usage:
AT+S.RESET<cr>
Parameters:
None
6.6 AT+S.PMS
The SPWF04Sx features different power states as a consequence of the different operating modes of the radio
and the STM32 microcontroller. This command is used to manage the module power state.
The table that follows summarizes the power state conditions supported by the module. The values of the
variables affecting the output of the command are also reported in the following table.
Table 4. Power states and configuration
Module state <Mode> option value STM32 state WLAN state AT variable default values
Active 0 Run
Rx Idle
Rx Active
Tx Active
AT+S.SCFG=sleep_enabled,0
AT+S.SCFG=wifi_powersave,0
AT+S.SCFG=standby_enabled,0
PowerSave (1) 1 Run PS or Fast PS
AT+S.SCFG=sleep_enabled,0
AT+S.SCFG=standby_enabled,0
AT+S.SCFG=wifi_powersave,1
Sleep(1) 2 Stop PS or Fast PS
AT+S.SCFG=sleep_enabled,1
AT+S.SCFG=standby_enabled,0
AT+S.SCFG=wifi_powersave,1
StandBy(2) 3 Standby Off AT+S.SCFG=standby_enabled,1
AT+S.SCFG=sleep_enabled,0
1. Variables wifi_beacon_wakeup, wifi_operational_mode, and wifi_listen_interval, need to be set to the desired value.
2. The variable standby_time to be set to the desired value.
Usage:
AT+S.PMS=[<mode>]<cr>
Parameters:
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<mode>
Default value: 0
Possible values:
• 0 → active mode
• 1 → powersave mode
• 2 → stop mode
• 3 → standby mode
6.7 AT+S.PYTHON
The command has a Python script executed when the file name is specified or allows to enter a Python shell
when the option is not used.
Usage:
1) AT+S.PYTHON<cr> to enter the MicroPython REPL shell.
2) AT+S.PYTHON=<filename><cr> to execute the specified script.
Parameters:
<filename> specifies the Python script to be executed. After the execution
of the script the command returns to the AT console.
6.8 AT+S.GCFG
This command lists all the configuration variables together with their current value.
Usage:
1) AT+S.GCFG<cr> to get the full list of configuration variables
2) AT+S.GCFG=<cfg_var><cr> to get the value of the specified variable
Parameters:
<cfg_var> configuration variable. Refer to Table 7. Configuration
variables for a complete list of the configurable variables.
Result:
AT-S.Var:<var>=<value>
<var> Specifies the configuration variable name
<value> Specifies the configuration variable value
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6.9 AT+S.SCFG
Command to set the value of the named configuration variable. The value is saved in the RAM until the command
AT+S.WCFG is used.
Usage:
AT+S.SCFG=<key>,<value><cr>
Parameters:
<key> variable to configure
<value> value to be set
6.10 AT+S.WCFG
Command to save the configuration set to the Flash.
Usage:
AT+S.WCFG<cr>
Parameters:
None
6.11 AT+S.FCFG
Command to restore the factory configuration variables from the Flash. It is mandatory to run a reset (HW or SW)
after a factory restore.
Usage:
AT+S.FCFG<cr>
Note: HW factory restore of the variables is performed by pulling the pin GPIO0 high at power-up (until the
“+WIND:1:Poweron” indication is printed). In order to use the HW factory reset (GPIO0 enabled) and
FWUPDATE at the same time, see Section 6.13 AT+S.FSUPDATE.
Parameters:
None
6.12 AT+S.FSWRITE
The command is used to update the external volume via serial interface.
Note: The HW flow control MUST be enabled in order to use the command via UART.
Usage:
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AT+S.FSWRITE=<length><cr>{data}
Parameters:
<length> Data length to send (in bytes)
6.13 AT+S.FSUPDATE
To download an updated file system from the named host and path. The downloaded image overwrites the
existing one. In this case, the user needs to perform a backup of the current file system.
Usage:
AT+S.FSUPDATE=<mem>,<hostname>,[<path&queryopts>],[<port>],[<TLS>],[<username>],
[<passwd>]<cr>
Parameters:
<mem>
specifies the memory where the file system is saved.
• e → user Flash
• i → application Flash
• x → external memory volume
<hostname> Target host. DNS resolvable name or IP address.
<path&queryopts> Default:/fs.img. Document path and optional query arguments.
<port> Default 80 (if TLS=0) or 443 (if TLS>0).
<TLS> Default: 0. Values range: 0 → unsecured; 1 → autodetect; 2
→ TLS
<username> Default: none.
<passwd> Default: none.
6.14 AT+S.FWUPDATE
This command downloads an updated firmware image located at the named host and path. The downloaded
image is temporary stored in the internal Flash. The user should perform a procedure to save the content of the
file system that will be overwritten during the process.
Note: FWUPDATE can be invalidated by pulling GPIO0 high during the first reset after the execution of AT
+S.FWUPDATE command. In this case, the external filesystem is erased and the FW update is not performed.
Usage:
Note: The HW factory reset pin (GPIO0) must be tight low during F/W update. The HW factory reset can be used after
“+WIND:17:F/W update complete!”
AT+S.FWUPDATE=e,<hostname>,[<path&queryopts>],[<port>],[<TLS>],[<username>],
[<passwd>]<cr>
Parameters:
<hostname> Target host. DNS resolvable name or IP address.
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<path&queryopts>
Default: /fw.fota. Document path and optional query
arguments. If a secure FOTA is required, the extension of the
file needs to be “.sfota”.
<port> Default 80 (if TLS=0) or 443 (if TLS>0).
<TLS> Default: 0. Values range: 0 → unsecured; 1 → autodetect; 2
→ TLS
<username> Default: none.
<passwd> Default: none.
6.15 AT+S.GPIOC
Command used to configure the function of the various GPIOs on the module. GPIOs can be configured as inputs
or outputs. When used as inputs, they generate an interrupt when the state changes that can be configured on
the signal edge.
Usage:
1) AT+S.GPIOC=<number>,out<cr> to configure a gpio as an output
2) AT+S.GPIOC=<number>,in,
[<interrupt>]<cr> to configure a gpio as an input
Parameters:
<number> GPIO Number (see Datasheet)
<interrupt>
Default: No interrupt (turn it off, if enabled). It can assume one
of the following values:
• R → Rising edge
• F → Falling edge
• B → Both rising and falling edges
6.16 AT+S.GPIOR
AT+S.GPIOR is used to read the value and the direction of a previously-configured GPIO.
Usage:
AT+S.GPIOR=<num><cr>
Parameters:
<num> specifies the GPIO to read
Result:
AT-S.Value:<num>:<level>:<direction>
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<num> Specifies the number of GPIO read
<level> 0 (low) or 1 (high)
<direction> 0 (output pullup) or 1 (input)
6.17 AT+S.GPIOW
AT+S.GPIOW is used to set the value of a previously-configured output GPIO.
Usage:
AT+S.GPIOW=<num>,<level><cr>
Parameters:
<num> specifies the GPIO to be set
<level> specifies one possible value(0|1) for the specified GPIO.
6.18 AT+S.DAC
The DAC command enables DAC on GPIO15.
Usage:
AT+S.DAC=<value><cr>
Parameters:
<value> must be set in mV (between 1 and 3300). The value=0
disables DAC on GPIO15
6.19 AT+S.ADC
AT+S.ADC returns ADC value on the selected GPIO. The value range is between 0 and 3300 mV with a
measurement accuracy of 10 mV.
Usage:
AT+S.ADC=<num><cr>
Parameters:
<num> specifies the GPIO to be used for conversion. Available
GPIOs are 0, 1 and 16
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Result:
AT-S.Value:<value>
<value> Specifies the ADC value
6.20 AT+S.PWM
The PWM command enables PWM on the selected GPIO, with a specified frequency and duty-cycle.
Usage:
AT+S.PWM=<num>,<frequency>[,<duty_cycle>]<cr>
Parameters:
<num> specifies the GPIO to be used for PWM. Available GPIOs are
2 and 4
<frequency> value between 1 and 10 kHz. The value=0 disables PWM
<duty_cycle> default: 50%. The value is in the 0 - 100 range.
6.21 AT+S.TIME
Command to get or set the time (date, time)
Usage:
1) AT+S.TIME<cr>
returns the current date in the format “AT-
S.Date:yy.mm.dd:nn” and the current time in the format “AT-
S.Time:hh:mm:ss”. The time refers to UTC format and must
be expressed as the time in seconds since 1970-Jan-01.
2) AT+S.TIME=<time> sets the time as specified by the parameter
Parameters:
<time> value to set the time. The time refers to UTC format and it
must be expressed in seconds since 1970-Jan-01.
Result:
AT-S.Date:<yy>.<mo>.<dd>:<day>
AT-S.Time:<hh>.<mi>.<ss>
<yy> Specifies the year
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<mo> Specifies the month
<dd> Specifies the day
<day> Specifies the year of the week
<hh> Specifies the hours
<mi> Specifies the minutes
<ss> Specifies the seconds
6.22 AT+S.RANDOM
Command that provides a random number generated by the peripheral integrated in the STM32.
Usage:
AT+S.RANDOM<cr>
Parameters:
None
Result:
AT-S.Number:<value>
<value> Specifies the 32-bit random number
6.23 AT+S.FSC
This command has effect in the RAM memory volume and external SD card volume. The command creates a file
in the selected volume or appends the data following the command in case the file already exists. The space
available in the file system in RAM can be set using ramdisk_memsize configuration variable. Minimum size is 2
Kb, resulting in maximum 2 files.
Usage:
AT+S.FSC=<filename>,<datalen><cr>{data}
Parameters:
<filename> name of the file. Max size is 64 bytes
<datalen> amount of space in bytes to allocate for the file
6.24 AT+S.FSD
The command has effect in the RAM memory volume and external SD card volume. The command deletes an
existing file.
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