INFICON SQC-222 Thin Film Deposition Controller - Manual (Page 72)

Chapter 5 Communications
5-2
The two character CRC is computed using the following algorithm:
1. The CRC is initialized to 3FFF hex.
2. Each character in the message is examined, bit by bit, and added to the CRC
in the following manner:
a) The character is exclusive or’d with the CRC.
b) The CRC is shifted right one bit position.
c) If the character’s least significant bit is a 0 then the CRC is exclusive or’d
with 2001 hex.
d) Steps b and c are repeated for each of the 8 bits in the character.
The CRC contains 14 significant bits. This is split into two characters of 7 bits each,
and then a decimal 34 is added to offset the character outside the range of the Sync
Character.
5.3 Commands
The examples represent the data commands only (less sync, length, and CRC
characters) for clarity. The Utility and Demo CDROM includes a demonstration program,
MessageGen.EXE, that allows you to view the complete send/receive commands.
Command: @
Parameters: None
Description: Returns the model number and software version number. Use this
command to test for correct communications with the instrument.
Example: @ SQC222 Ver 1.0
Command: A
Parameters: [1..9], Values | ?
Description: Film parameters. The parameters available for change or inspection are
Label, Density, Tooling, Z-Factor, Final Thickness, Thickness Setpoint,
Time Setpoint, Sensor Average