INFICON STC-2000A Thin Film Deposition Controller Operating Manual - Manual (Page 199)

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STC-2000A DEPOSITION CONTROLLER
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After the proper cable is made or purchased, make sure the baud rate of the computer and STC-
2000A are the same. This is done by going into the Executive Menu (by pressing the fixed MENU key,
followed by the EXECUTIVE MENU key) and selecting the communications setup option. You will see a
screen with the current baud rate on it. Section 6.4 describes programming these parameters in detail.
Setting The Baud Rate
Make sure that the baud rate on your computer is set to the same baud rate. The STC-2000A is
shipped from the factory set at 9600 baud. To set an IBM-PC to the same baud rate, at a DOS prompt type
in:
Mode Com1:9600,N,8,1
This will set the IBM for 9600 baud, 8 data bits, no parity, and 1 stop bit on its COM1 port. It is
important to use 8 data bits because the protocols use all of them.
SECTION 6.1 Sycon Protocol
The STC-2000A does not initiate any messages on its own. It responds only when "spoken" to. In
order for error-free communications to occur, several safeguards are built into the Sycon protocol for
checking data integrity. The general format for sending and receiving commands is:
(STX) (Data Length) (Data(Data..Data)) (Checksum)
RS-232 Message Format
The STX character (hex 02) indicates a start of message sequence. The STC-2000A uses this as a
synchronization point. It just sits in a loop waiting for the STX character. If a different character is
received, it is discarded. When the STX character is received, the STC-2000A looks at the rest of the
characters in the command.
The data length is a ASCII character from SOH (1 decimal) through CR (13 decimal) and
indicates the number of data characters in the message. The data is defined in the protocol below. The
STC-2000A uses this number to determine where the end of the command is. If there is a mismatch
between this number and the actual number of data characters in the message, one of two things can
happen. If the data length number is low, the STC-2000A will terminate the command prematurely. The
checksum will not match and an error will be recognized by the STC-2000A. It will not respond in any
way.
Message Length
If the data length number is high, the STC-2000A will be waiting for more characters than actually
contained in the message. In order to recover from either kind of error, the host computer must have a
time-out/retry capability built into the software. There is a maximum of 13 data characters allowed in any
communications message. This does not include any packet formatting characters.
Checksum - Error Recovery
The checksum is the sum (modulo 256) of only the data bytes. If this does not match the actual
checksum of the data, an error condition is recognized by the STC-2000A. It will not respond to the
command.
Table 6.1 is a basic program that will run on an IBM-PC. It prompts you for a command to send
to the STC-2000A and will print the response on the display. It is written in BASICA program, but will
also run under Microsoft GWBASIC. This program prompts the user for the STC-2000A command; then
adds the STX, data length and checksum before it transmits the message to the STC-2000A.
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