KSE-91A Network Attach
The KSE-91A is an external LTE-M / NB-IoT modem running Nordic Semiconductor's Serial Modem firmware, controlled with AT commands over its USB-C / UART / RS232 / RS485 interface. It is set up to attach to the cellular network automatically at power-on, and its built-in display shows the progress — for most users there is nothing to configure.
Most of the time you don't need this page — power the modem, connect the antenna, and watch the display reach Connected. Come here only to confirm the attach over AT, to switch the radio mode (LTE-M vs NB-IoT), or to attach manually with a custom APN.
How Attach Works by Default
At power-on the modem brings up the radio and registers on the network on its own. The display walks through the sequence:
| Screen | Meaning |
|---|---|
| Boot | Powering up: shows product and firmware version |
| Starting | Modem is initializing |
| Connecting | Searching for and attaching to the network (up to ~1 minute) |
| Connected | ✅ Online and attached — normal operating state |
The Connecting screen is normal during startup. Wait until the modem reaches Connected or shows a clear fault screen (see Troubleshooting).
Confirm the Module Attached (over AT)
If you are driving the modem from a host, confirm attach over the serial interface instead of the display.
1. Check Registration Status
AT+CEREG?
+CEREG: 1,1
OK
The second value is the registration status:
+CEREG status | Meaning |
|---|---|
1 | ✅ Registered — home network |
5 | ✅ Registered — roaming |
2 | Still searching — wait a moment |
0 / 3 / 4 | Not attached — see manual attach below |
2. Check Signal and IP
AT+CESQ
+CESQ: 99,99,255,255,20,54
OK
AT+CGPADDR
+CGPADDR: 0,"10.0.0.1"
OK
Aim for RSRP better than −110 dBm. An assigned IP from AT+CGPADDR confirms the data connection is up.
Set the Radio Mode (LTE-M or NB-IoT)
This is the setting most users configure. Use AT%XSYSTEMMODE to choose which radio access technology the modem uses:
AT%XSYSTEMMODE=<LTE-M>,<NB-IoT>,<GNSS>,<preference>
| Parameter | Meaning | Value |
|---|---|---|
<LTE-M> | Enable LTE-M | 1 = on, 0 = off |
<NB-IoT> | Enable NB-IoT | 1 = on, 0 = off |
<GNSS> | Enable GNSS | 1 = on, 0 = off |
<preference> | Which to prefer when both are on | 0 none · 1 LTE-M · 2 NB-IoT |
Common presets:
AT%XSYSTEMMODE=1,1,0,1 LTE-M + NB-IoT, prefer LTE-M (typical)
AT%XSYSTEMMODE=1,0,0,0 LTE-M only
AT%XSYSTEMMODE=0,1,0,0 NB-IoT only
Change the system mode with the radio off, then bring it back online:
AT+CFUN=4 Go offline
AT%XSYSTEMMODE=1,1,0,1 Set the radio mode
AT+CFUN=1 Go online; attach begins
Manual Attach
Use this only if your SIM needs an APN different from the default, or the modem did not attach on its own.
1. Go Offline and Configure
AT+CFUN=4 Go offline
AT%XSYSTEMMODE=1,1,0,1 Choose the radio mode
AT+CGDCONT=0,"IP","<your-apn>" Set the APN
2. Go Online and Attach
AT+CFUN=1 Go online; attach begins
AT+CEREG=5 Subscribe to registration updates
AT+CEREG? Poll until status is 1 or 5
3. Verify the Checkpoints
| Checkpoint | Command | Pass Condition |
|---|---|---|
| Registered | AT+CEREG? | status 1 or 5 |
| Signal OK | AT+CESQ | RSRP better than −110 dBm |
| Data up | AT+CGPADDR | non-empty IP address |
Troubleshooting
| Symptom | Likely Cause | Recommended Action |
|---|---|---|
| Display stuck at Connecting | Weak coverage / band not supported | Reposition antenna; confirm operator LTE-M / NB-IoT support |
| No Signal screen | No mobile coverage | Move the modem or antenna to a better reception area |
| Check SIM screen | SIM missing or unreadable | Power off, reseat the SIM, power on again |
| Service Error screen | Network reached but connection refused | Check SIM plan/service; collect Diagnostics information |
+CEREG: ...,3 (denied) | SIM not provisioned / wrong APN | Verify data plan; set the APN manually |
| Registered but no IP | PDP context inactive | Re-check the APN; confirm the plan allows data |
For registration error codes in depth, see the FAQ.
Related Resources
- Quick Start — hardware bring-up and display screens
- AT Commands — full command reference
- FAQ — registration troubleshooting