Snell & Wilcox Supervisor LX, Operation & Installation Manual

Page: 51 / 59

SuperVisor LX SECTION 6
FGAX3249400MANAA 100701 Version 1 Issue 2 6.3
Rollcall
   
This is Snell & Wilcox’s proprietary communications protocol. It is used to remotely control the Supervisor LX.
Physical connection to the Supervisor LX is made via it’s RS422 connector. The RS422 port is factory set at
38 Kbaud but can be reconfigured for lower rates.
Rollcall

operates in binary computer mode. A start of packet (STX), end of packet (ETX) and control
characters are used for binary transfers to the Supervisor LX. Whenever the Supervisor LX receives an STX
character, the following data is treated as pure binary data until the reception of an ETX character. The reply
from the unit will also be in binary mode for each command.
Char Definition Description
0x02 STX Start of packet
0x03 ETX End of packet
0x1B ESC Escape character for STX, ETX and ESC
An escape sequence is used if the start, end or escape control code values are required in the body of the
packet.
The escape character is inserted, and the desired character has its MSB inverted.
The table below shows the 2 byte replacements.
Value required in Packet. Sequence of bytes to be sent
0x02 0x1B, 0x82
0x03 0x1B, 0x83
0x1B 0x1B, 0x9B
Rollcall
   
Packet Types
The packet types of interest for Supervisor LX control are:
SetParam (SP_SETPARAM)
GetParam (SP_GETFSTAT)
RetParam (SP_RETFSTAT)
Wait (SP_WAIT)
SetParam packets are sent to the Supervisor LX from the control software and are used to set new values for
commands eg. set Black Level to 0.
GetParam packets are sent to the Supervisor LX from the control software and are used to request the current
values of commands eg. What is the current input channel?
RetParam packets are returned from the Supervisor LX in response to both SetParam and GetParam packets.
They serve two purposes. Firstly they are used for flow control ie. when a RetParam is received by the control
software it means that the Supervisor LX is ready to receive another command. Secondly the RetParam
packet is used to return the current value of the command specified in the previous Set or GetParam packet.
Wait packets can be returned from the Supervisor LX in response to a SetParam packets. They are used to
indicate to the control software that the command will take a longer than normal time to complete. The Wait
packet contains the expected delay, in seconds, before a RetParam packet will be issued.