INFICON MDC-370 Thin Film Deposition Controller - Manual (Page 133)

MDC-370 DEPOSITION CONTROLLER
The checksum is the compliment of the one byte sum of all bytes from, and
including, the instruction code to the end of the message. If the one byte sum of
all these bytes is added to the checksum, the result should equal 255.
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.
11.6 DATA TYPES
There are three data types stored in the MDC-370: 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 either 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)
where DP is 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.
11.7 MESSAGE RECEIVED STATUS
Following the receipt of each message, the controller 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. The following table shows a list of possible receive codes:
Receive Code Description
0 Message received O.K.
1 Invalid checksum.
2 Invalid instruction code.
3 Invalid message length.
4 Parameter(s) out of range.
COMPUTER INTERFACE 11-3