Sync Bytes : the key concepts of  T5A packet

LXSDF T5A packet uses initial 5 bytes for each packet transmission as “Purpose for Synchronizing Packet”. The first four bytes are allocated the fixed value 255(0xFF in hex), and fixed 254 (0xFE in hex) for fifth byte. Namely, Sync Bytes are designed only in the spots where appear 255, 255, 255, 255 and 254 sequentially in the whole packet byte arrays.

Receiving side should check each byte and extract the “Sync Bytes”, so it can find the starting spot of 1 packet. Once finding the starting spot, it is able to extract the data needed in the program under the packet Standard..

The following picture indicates that the orange color part in the one packet is assigned “Sync Bytes” and then a series of bytes for one packet.

 

T5A Packet Definitions

The table shows the definitions of T5A packet. Each index is one byte and transmitted in order when transmitting serial. An available value for each packet index, the terms of the packet elements.

Table. LXSDF T5A Packet Definitions.
 Index  Value  Packet Element Name for Stream Mode.  Packet Element Name for Non-Stream Mode.
 0  255  SyncByte0 (Synchronization Byte 0)
 1  255  SyncByte1 (Synchronization Byte 1)
 2  255  SyncByte2 (Synchronization Byte 2)
 3  255  SyncByte3 (Synchronization Byte 3)
 4  254  SyncByte4 (Synchronization Byte 4)
 5  0~254  PPD (Packet Property Data). 0~15 : Stream Mode, 16~254 : Non-Stream Mode.
 6  0~255  PCDT (PCD Type) : Bit 2,1,0.  PBS (Packet Byte Size)
 7  0~255  PC (Packet Count)  IID (Information ID)
 8  0~255  PCD0 (Packet Cyclic Data 0) LSByte  .
 9  0~255  PCD1 (Packet Cyclic Data 1) MSByte  .
 10  0~253  PCD SEP   reserved.
 11  0~255  PUD0 (Packet Unit Data 0) LSByte
 12  0~255  PUD1 (Packet Unit Data 1)
 13  0~255  PUD2 (Packet Unit Data 2)
 14  0~255  PUD3 (Packet Unit Data 3) MSByte
 15  0~253  PUD SEP  reserved.
 16  0~255  PSD0 (Packet Stream Data 0) LSByte  .
 17  0~255  PSD1 (Packet Stream Data 1)  .
 18  0~255  PSD2 (Packet Stream Data 2)  .
 19  0~255  PSD3 (Packet Stream Data 3) MSByte  .
 20  0~253  PSD SEP  .
 …  …  Can be repeated above 16~20 index  .
 Color  Description
 Common packet elements for both Stream Mode and Non-Stream  Mode
 Data placement for multi channel stream data. Freely expandable to any number of channels. The typical example of the multi channel stream data is the continuous output of a multi channel ADC(Analog to Digital Converter).

 

Difference between Stream & Non-Stream Mode

Packet Index  Stream Mode  Non-Stream Mode
 5  PPD :  available value 0 ~ 15  PPD : available value 16 ~ 254
 6  PCDT : Packet Cyclic Data Type.  PBS : Packet Byte Size allocated.
 7  PC : +1 for each packet.  IID : Information ID allocated.
 8 ~ 10  PCD0,1,PCD SEP : PCD data is allocated each PC.  general data allocated.
 11 ~ 15  PUD0,1,2,3,  PUD SEP : Packet Unit Data.  general data allocated.
 16 and over  PSD :  real time stream data allocated.  general data allocated.

Packet Byte Size 

  • Stream Mode : Predefined fixed value. ex. 16, 32, …, etc  depends on applications.
  • Non-Stream Mode : Determined  by packet index 6( PBS ) per each packet.