Summary
As stated in Dragino website user guide on LHT65N (link), by enabling SYNCMOD=1(Default) and PNACKMD=1, “In a future uplink if LHT65N/S gets a ACK, LHT65N/S will consider there is a network connection and resend all NONE-ACK messages”. So recovery of the samples during disconnection period happens automatically; but that’s not the case that I witnessed!
I must also mention that I have deployed this feature on Dragino S31B-LB devices and it worked correctly as expected.
Logs
As explained in the guide (Section2.6.5), Datalog Uplink payload is as below:
I realized that the issue is in bit no.6 of “Poll message flag & Ext” byte. Having SYNCMOD and PNACKMD enabled, I saw that after a period of disconnection the samples of that period are correctly sent in an uplink after reconnection and receiving the ACK. Below is an example of a datalog:
“frm_payload”: "f/8J9wHSgWpTlQJ//wn5AdmBalOVD3//CfkB1oFqU5Ubf/8J+wHRgWpTlSd//wn7AdWBalOVM3//CfsBz4FqU5U/f/8J+QHSgWpTlUs=”
payload converted from base64 to hex:
7fff09f701d2816a5395027fff09f901d9816a53950f7fff09f901d6816a53951b7fff09fb01d1816a5395277fff09fb01d5816a5395337fff09fb01cf816a53953f7fff09f901d2816a53954b
I take the first sample as an example: 7fff09f701d2816a539502
and if we take the “Poll message flag & Ext” byte (in this example: 81) and convert it to binary, we get: 1000 0001
As you can see “Poll Message Flag” is 0(!) while the format of the uplink is clearly a datalog one!
This issue has caused the uplink payload decoder to fail recovering these samples.
I must repeat that the same feature works on Dragino S31B-LB with “Poll Message Flag” being 1 when it is recovering a datalog.
Hardware
I am using an LHT65N with config below:
AT+ADR=0
AT+TXP=0
AT+DR=5
AT+DCS=0
AT+PNM=1
AT+RX2FQ=869525000
AT+RX2DR=3
AT+RX1DL=5000
AT+RX2DL=6000
AT+JN1DL=5000
AT+JN2DL=6000
AT+NJM=1
AT+NWKID=00 00 00 00
AT+FCU=12
AT+FCD=6
AT+CLASS=A
AT+NJS=1
AT+RECVB=0:
AT+RECV=
AT+VER=EU868 v1.3
AT+CFM=1,0,0
AT+SNR=0
AT+RSSI=0
AT+TDC=600000
AT+PORT=2
AT+PWORD=123456
AT+CHS=0
AT+SLEEP=0
AT+EXT=1
AT+BAT=2789
AT+WMOD=0
AT+ARTEMP=-40,125
AT+CITEMP=1
AT+RJTDC=20
AT+RPL=2
AT+TIMESTAMP=systime= 2026/7/12 13:33:54 (1783863234)
AT+LEAPSEC=18
AT+SYNCMOD=1
AT+SYNCTDC=1
AT+PID=0
AT+DDETECT=1,57600,59040
AT+SETMAXNBTRANS=1,0
AT+UUID=0A045C2F01322402
AT+PNACKMD=1
AT+EPLOGIC=0