Lord Corporation MSLINK0003 User Manual
SerialLink Manual
Serial-Link Serial Packet Protocol (SPP) Draft version
1.20, for Internal MicroStrain use only
1.20, for Internal MicroStrain use only
Working Draft: 8/7/2012
Overview
The Serial-Link Serial Packet Protocol (SPP) defines a standard for delivery of data and
commands over the Serial-Link UART communications pipeline. To communicate,
each device is capable of reading, responding to, and forwarding an SPP Packet. Any
device may originate a message and receive a reply from any other device. A single
packet may be delivered to multiple devices. If a device does not exist on the pipeline,
or is incapable of responding to a particular packet, it replies with an error, but will
propagate the packet to the next device, if it exists, so that the next device may respond to
the packet. The protocol to send a packet is shown below.
commands over the Serial-Link UART communications pipeline. To communicate,
each device is capable of reading, responding to, and forwarding an SPP Packet. Any
device may originate a message and receive a reply from any other device. A single
packet may be delivered to multiple devices. If a device does not exist on the pipeline,
or is incapable of responding to a particular packet, it replies with an error, but will
propagate the packet to the next device, if it exists, so that the next device may respond to
the packet. The protocol to send a packet is shown below.
Hardware UART specifications
115,200 bps, no parity, 8 data bits, 1 stop bit
Packet Description
The basic structure of the SPP Packet looks like this:
Start Of Packet (SOP):
0xAA
Delivery Stop Flags:
<1 byte>
App Data Type:
<1 byte>
Node
Address:
<2
bytes>
Application data Length:
<1 byte>
Application data:
<0 to 100 bytes>
CheckSum:
<2
bytes>
The size of the packet is always AppDataLength + 8 (except for a variant – see Packet
Variants) and the checksum is always the last 2 bytes (even for variants).
Variants) and the checksum is always the last 2 bytes (even for variants).
Start Of Packet (SOP) (1 byte: Pkt[0]):
The start of packet is a single byte of the value 0xAA (or binary 10101010)
Delivery Flags (1 byte: Pkt[1])
Delivery flag instructs the receiving device how to act upon reception of the packet.
This is currently fixed at a hex value 01H which instructs the receiving device to forward
the received packet over its UART.