Sync Bytes : the key concepts of  LXSDF T2 Tx packet

LXSDF T2 Tx packet uses initial 2 bytes for each packet transmission as “Purpose for Synchronizing Packet”. The first byte is allocated the fixed value 255(0xFF in hex), and fixed 254 (0xFE in hex) for second byte. Namely, Sync Bytes are designed only in the spots where appear 255 and 254 sequentially in the whole packet byte arrays.

Receiving side should check each byte abd 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 TX packet Standard.

The following picture indicates that the orange color part in the first 1 packet is assigned “Sync Bytes” and then a series of bytes for one packet.

LXSDF T2 Tx Packet Definitions

The table shows the definitions of T2 Tx packet. Each index is one byte and transmitted sequentially in order when transmitting serial data. An available value for each packet index, the terms of the packet elements.

Table. LXSDF T2 Tx Packet Definitions.
 Index  Value  Packet Element Name 
 0  255  SyncByte0 (Synchronization Byte 0)
 1  254  SyncByte1 (Synchronization Byte 1)
 2  0~254  PUD0 (Packet Unit Data 0)
 3  0~127  CRD (Command Response Data). bit 6
 PUD2 (Packet Unit Data 2). bit 5,4,3
 PCDT (Packet Cyclic Data Type). bit 2,1,0
 4  0~255  PC (Packet Count)
 5  0~127  PUD 1 (Packet Unit Data 1)
 6  0~255  PCD (Packet Cyclic Data)
 8  0~253  PSD1 (Packet Stream Data High Byte)
 9  0~255  PSD0 (Packet Stream Data Low Byte)
 10  0~253  PSD1 (Packet Stream Data High Byte)
 11  0~255  PSD0 (Packet Stream Data Low Byte)
 …  …  …
 N-1  0~253  PSD1 (Packet Stream Data High Byte)
 N  0~255  PSD0 (Packet Stream Data Low Byte)
 Color  Description
 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).


PC (Packet Count)

+1 for every one packet transmission and start 0 again after the maximum value.
By using PC, it is necessarily used to identify the data transmitted to PCD every packet.
The maximum of PC value gets different value according to PCD Type value. If PCDT is 0, PC maximum is 31.

CRD (Command Response Data)

If the device receives the command from the other device, CRD value is reversed.
Usage – If CRD value is 1 before transmitting the order from host and the value is the same after transmitting,
the order transmission is failed. If CRD value is changed, it means the device receives the order from host

PUD 0, PUD 1, PUD 2 (Packet Unit Data)

Allocated data is different for each product. Mainly, information data to transmit at high speed is allocated.

PCDT (Packet Cyclic Data Type)

PC maximum depends on this value and data transmitted to packet cyclic data depends on PCDT value. PCDT value is always 0 for the first stage(device power ON) and though PCD mode value is changed into different value like 1,2,3.. on the situation, it is changed into 0 automatically by completing data transmission of the mode one time.

 PCDT  PC (Packet Count) Maximum  Data
 0  31  Exclusive data for LXSDF T2 and general data.
 1  depends on each product.
 2  depends on each product.
 3  depends on each product.
 4  depends on each product.
 5  depends on each product.
 6  depends on each product.
 7  depends on each product.


LXSDF T2 PCD Designated Data for PCDT 0.

The section from PC 0 to 19 is for transmitting product’s specialized data and the section from PC 20 to PC 31 is for system designated data. The system exclusive data is explained as below table.

 Table. PCD Designated Data of PCDT 0
 PCD[PC]  Item  Description
 PCD[31]  Com port search information  fixed value 108. Information for searching device using LXSDF T2.
 PCD[30]  LXDeviceID  Allocated value between 1 and 255. Unique ID for identifying the device.
 PCD[29]  ComFirmInfo1  Firmware ID and version for processor 1.
 PCD[28]  Number of channel  Number of channel from stream area of packet.
 PCD[27]  Number of samples  Number of samples from stream area of packet.
 PCD[26]  ComPath  Communication physical path.
 PCD[25]  ComFirmInfo2  Firmware ID and version for processor 2.
 PCD[24]  ComFirmInfo3  Firmware ID and version for processor 3.
 PCD[23]  –  – reserved
 PCD[22]  –  – reserved
 PCD[21]  –  – reserved
 PCD[20]  –  – reserved


ComPath is used for mark to show what physical path to transmit data. It is possible to transmit more than two communication path in one device. The host received the data refers to Compath value to check the communication path.

 ComPath Value  Communication Path
 0  UART
 2  Bluetooth SPP(Serial Peripheral Profile)
 3  Bluetooth Low Energy SPS