Maximum payload

DigiMesh uses the 802.15.4 PHY layer including a 2-byte CRC at the end of the frame. This reduces the size of each frame to 125 bytes. After the MAC header, the NWK header, and the APP header are included at the beginning of the packet, the remaining space is 73 bytes for payload. If CTR mode encryption is enabled, this number is further reduced to 65 bytes. The best way to determine the maximum payload is to read NP (Maximum Packet Payload Bytes).

Sending a packet securely across a Secure Session (API transmit option bit 4 enabled) reduces the maximum payload size by 4 bytes.

These maximums only apply in API mode. If you attempt to send an API packet with a larger payload than specified, the device responds with a Transmit Status frame (0x8B) with the Status field set to 74 (Data payload too large).

In Transparent mode, the firmware splits the data as necessary to cope with maximum payloads.