Product Info

IR LRM2 Radio Module

Functional Description

Document p/n: 9S02-9027-A001 Rev.A

Host

LRM Radio Module

Host Data Buffer Tx/Rx

Transmit Telegram Frames

Receive Telegram Frames

RF packets

LRM Host Interface LRM RF Interface

Figure 4.2 - Data communication model

- The IR LRM2 Radio Module is used to communicate telegrams between hosts. In Unity context, hosts are

OCU and MCU CPU boards. The IR LRM2 has two interfaces: a Host Interface and a RF Interface.

- Transmit and Received Telegrams are relayed through the IR LRM2 Host Data Buffer. This buffer is

capable to hold only one telegram at a time. The purpose of this buffer is to relax host timings

requirements, and to allow decoupling between Host Interface and RF Interface data rates.

- Telegrams sent/received on the Host Interface and RF interface are encapsulated into frames to improve

synchronization.

- The IR LRM2 does not perform any processing on the telegrams content; it controls only the frames

overhead.

4.2 Telegram Transmission

Transmit frames have two fields:

- Telegram length (number of bytes). The length is used by the CPU to control the transmission process.

- Telegram (maximum 254 bytes). The content of the telegram is defined by the application. For Unity

application, this is the Unity Telegram beginning with the Scrambling byte, the TID and terminated with the

16bits CRC, as defined in ref [2].

Length

1 byte

“Length” bytes

Figure 4.3 - Transmit Telegram frame format

4.3 Telegram Reception

Each RF packet received by the LRM2 is sent to the host interface, followed by its RSSI. Also, in order to ensure

receive telegram frame synchronization (i.e. unambiguous detection of the start of the frame), the frame is

encapsulated according to SLIP framing. SLIP framing is very simple to decode. It is described in section Error!

Reference source not found..

Receive frame fields are:

- SOF (Start-of-Frame character). This is part of SLIP encapsulation.

- Length of the Telegram field (number of bytes), not counting RSSI fields and any additional control characters

introduced for SLIP encapsulation.

- Telegram (maximum 254 bytes). The content of the telegram is defined by the application.