INFICON TM-400 Thin Film Deposition Monitor - Manual (Page 69)

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TM-350/400 Operating Manual
If the sum of all bytes occupies more than one byte, a single byte checksum can
be generated using the expression: checksum=! (Sum MOD 256), i.e. the
checksum is the complement of the remainder byte, which results from dividing the
sum of all bytes by 256.
10.6 Data Types
There are three data types stored in the TM-350/400: One byte, two byte, and three
byte parameters. All data types are stored as integers in binary format with the
most significant byte first. The one-byte data types are ASCII characters, numeric
values (0-255), or 8 bit registers. Some of the multiple byte data types are decimal
values stored as integers. To convert these values to their decimal equivalent, use
the following equation:
Decimal Value = (Integer Value)/(10*DP) [1]
Where:
DP = the value’s decimal point position.
The decimal point positions for all the parameters are constant and are given in
tables along with the parameters’ range.
10.7 Message Received Status
Following the receipt of each message, the monitor will send a one-byte ‘received
status’ message, indicating how the message was received, with the following
format:
Header
Address
Inst=253
Length=2
Instruction Code
Receive code
Checksum
A value of 253 for the instruction byte indicates that this is a received status
message. The Instruction Code byte indicates the instruction code of the
message that was received.
Table 10-1 shows a list of possible receive codes.