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The RapidConnect serial protocol v2.0 has a frame-based architecture. All communication between the Host and Module is facilitated by the exchange of data frames. 

Serial Interface Parameters

The serial UART interface uses the following parameters: 

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Table 1: RapidConnect Serial Parameters

ParameterValue
Baud Rate115200
ParityNone
Stop Bits1
Data Bits8


Excerpt

Frame Structure

Every RapidConnect frame has the structure illustrated below:

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Header

The frame header is a fixed 5 bytes in length. Each byte is described in Table 2.

Table 2: Frame Header Description

ByteField NameDescription
0Start of Frame

Fixed value of 0xF1; will be referred to as START_OF_FRAME throughout this document. 

1Primary Header

Defines the primary frame type.

2Secondary Header

Identifies the command subset of the given primary frame type.

3Frame Sequence Number

0 – 127: Host initiated transactions 

128 – 255: Module initiated transactions 


The Frame Sequence Number enumerates a serial message exchanged between the Host and the Module, and vice versa. Use of a Frame Sequence Number for each such message is recommended.

For best practice, we also recommend the Frame Sequence Number be incremented by 1 for each newly initiated message.

Any transaction, whether initiated by the Host or the Module, may be acknowledged (i.e., ACK'ed) by the recipient with a response using the same Frame Sequence Number.

The Frame Sequence Number is used for tracking purposes but is not a mandatory feature. If its use is not desired, it should be assigned a value of 0x00. 

4Payload LengthDefines the length of the payload of a received or transmitted frame as 0-n bytes; at the time of this writing, the maximum acceptable

values for n are:


Transmitted by Module – 0x7A or 122 bytes

Received by Module – 0x7A or 122 bytes 


Payload

Unlike the header, the payload is of variable size, ranging from 0 to n bytes; the size is based on the Payload Length field in the header. All fields contained in the payload are ordered with the least significant byte first.

The payload contains the command’s parameters. Command parameters are detailed in Frame Payload Definitions.

Checksum

The Checksum is a fixed two bytes in length, with the MSB indicating the End of Frame (EOF). It is calculated by summing the values of byes starting from the Primary Header to the end of the Payload. Any overflow above two bytes is discarded.

The checksum calculation (CS) is given here:

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