Espressif Systems ESP User Manual

Chapter 3. application solution
3.9.7 Do I need to connect a router for communication between ESP-NOW devices?
ESP-NOW interacts directly from device to device and does not require a router to forward data.
3.9.8 Why does ESP-NOW limit the data length of each packet to 250 bytes? Can it be
congured?
• The maximum length does not support con󰝘guration. ESP-NOW uses one vendor-speci󰝘c element 󰝘eld of
action frame to transmit ESP-NOW data, whose length 󰝘eld is only 1 byte (0x󰝗 = 255) as de󰝘ned by IEEE
802.11. Thus, the maximum length of ESP-NOW data is limited to 250 bytes.
• Alternatively, you may try with API
esp_wifi_80211_tx()
to send and use sni󰝗er mode to receive. This
way could ful󰝘ll the need of working only base on Wi-Fi stack without involving TCP/IP stack.
3.9.9 What should I pay attention to when using ESP-NOW applications?
• The device cannot switch channels after connecting to Wi-Fi. It can only transmit and receive data on the
current Wi-Fi channel.
• After the device enters Modem-sleep mode, it cannot receive data from ESP-NOW.
3.9.10 How can I reduce power consumption when using ESP-NOW?
You can use the following methods to reduce power consumption:
• If you use ESP-IDF in versions earlier than v5.0, when the AP is not connected, you can
con󰝘gure the wake-up window size and interval using the esp_now_set_wake_window() and
esp_wi󰝘_set_connectionless_wake_interval() functions respectively to save power.
• If you use ESP-IDF v5.0 or the latest master version, the functions are di󰝗erent from the other
versions. Whether the AP is connected or not, you can use the esp_now_set_wake_window() and
esp_wi󰝘_connectionless_module_set_wake_interval() functions to set the wake-up window size
and interval, respectively.
• Note that the issue of window synchronization between the sending end and receiving end needs
to be considered in the application layer design. In this way, the chip will wake up at every“inter-
val”and work for a period of time equalling the value of “window size”. Under this situation,
you also need to con󰝘gure CONFIG_ESP_WIFI_STA_DISCONNECTED_PM_ENABLE=y in
sdkcon󰝘g.defaults.
3.9.11 In addition to wireless communication through ESP-NOW, is there any other bet-
ter way to realize one-to-one and one-to-many communication?
One-to-one and one-to-many communication can also be realized by using SoftAP + Station. The master
device applies Wi-Fi SoftAP mode to establish connections with multiple slave devices (Wi-Fi Station)
at the same time.
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Espressif Systems ESP Specifications

General

Brand	Espressif Systems
Model	ESP
Category	Motherboard
Language	English