RDR-N Payload Description (DRAFT)

This document describes the Payload of the Parametric ReorderDirect™ NFC Reader with LoRaWAN™

General Information

RDR-N devices are sending Data from NFC Tags held to the surface of the device. Data includes the timestamp of the scan, the serial number of the tag as well as one NDEF file stored on the tag.

Limitations

Due to the limited data capacity of LoRaWAN networks, readings may be buffered and sent later. When buffering scan records the device will append multiple records to the payload to empty the buffer as fast as possible.

Scan Record Data Structure

The LoRaWAN™ payload is generated by appending one or more scan records, delimited by the form feed escape command 0x0C. Payload length depends on the length of all scan records.

PCR2 Function Demonstration

LoRaWAN Application Payload Format

RDR-N devices will uplink a payload on each scan. If buffer is full multiple scan records will be appended to the payload intermittent by a 0C.

Byte Property Description Data Range (Hex string) Example
0 VID Vendor ID, always 0xbe for Parametric Devices be be
1 DEV_FAM Device Family, always 0x01 for PCR2 Devices 05 05
2 PL_REV Payload Revision 00 00
3:6 ULTS Uplink Timestamp (Unix Epoch) 00000000-FFFFFFFF 5F9BEB2C
Friday, 30. October 2020 10:30:04
7 RCNT Number of records in this payload 00-09 01
8 BUFF Number of records still in the buffer 00-ff 00
9… SR Scan Records
(see below)
variable length  
  EOSR End of Scan Record
always 0x0C
0C 0C


Scan Record

Scan records include the scan time, the serial number of the NFC tag and a variable length payload.

Offset Property Description Data Range (Hex String) Example
0:3 Scan Time Uplink Timestamp (Unix Epoch)
3 Bytes
00000000-FFFFFFFF 5F9BEB2C
Friday, 30. October 2020 10:30:04
4:11 NFC Serial NFC Serial number
8 Bytes on NDEF213
0000000000000000-FFFFFFFFFFFFFFFF 9EAF5126002302E0
12 Record Length NDEF File Length
0 if no NDEF file on tag
00-FF 01
13: Record Payload NDEF File data variable length  

Scan Records vs LoRaWAN™ Payload Length

When the buffer contains more than one scan record, the device will pack as many scan records into the LoRaWAN™ payload as possible. The firmware takes care to not exceed the max LoRaWAN™ payload length allowed in the current situation.

Data Rate Maximum LoRaWAN™ payload size allowed
air time limits
Scan record size
NDEF Payload “Hello”
Max Scan Records per Uplink
0 59 24 2
1 59 24 2
2 59 24 2
3 123 24 5
4 230 24 9
5 230 24 9
6 230 24 9
7 230 24 9

Port 5

RDR Uplink payloads are send on Port 5

Timestamp

RDR devices include a real-time clock (RTC) that will start at 0 after power up and will be synchronized with the DeviceTimeRequest Mechanism if available. See LoRaWAN® Application Layer Clock Synchronization. After synchronization the device will return Unix Epoch Timestamps. See Unix Epoch time format converter

ADR

RDR uses the automatic data rate adaption (ADR) function. Nevertheless HF performance can not be guaranteed when using LoRaWAN™ networks. It’s therefore a good idea to go expect the worst case.

See LoRaWAN™ 1.0.2 Regional Parameters Document for more information.