User manual

Computer Gateway User Manual 4-10 5/96
4.1.4
The CG handles necessary conversions to/from the DPS6 or IBM format from/to the
format used by devices on the LCN (IEEE 754).
INTEGER—Each integer value occupies one 16-bit word with a value range of -32767 to
32767. History messages also include 32-bit integer values for sample counts.
ASCII—Each ASCII value consists of a 24- or 40-byte ASCII string. A string of question
marks is used to specify a "doubtful" ASCII value.
ENUMERATION—There are two ways to represent enumerated values; as strings of eight
ASCII characters or as ordinal (integer) values. The choice of representation is made
within the various get/store data messages.
TIME—The CG has access to three representations of LCN time.
• LCN external time consists of an 18-byte ASCII string whose format is
MM/DD/YY∆HH:MM:SS∆ (where "∆" represents a space).
• LCN internal time is contained in three 16-bit words. The first two words form a 32-
bit unsigned integer that contains a count in seconds since 00:00:00 on January 1,
1979. The third word is an integer value that represents the count of tenths of
milliseconds in the current second.
• Timestamps returned with history data consist of 32-bit unsigned integers that contain
the count in seconds since 00:00:00 on January 1, 1979.
EXTERNAL ENTITY ID—(Read Only) Consists of an up-to-16-character ASCII string that
names an LCN-resident entity (used for CL program dynamic indirection). This is
followed by two ASCII characters that identify the LCN.
INTERNAL ENTITY ID—Consists of four 16-bit words containing the internal identification
of an LCN-resident entity (used for CL program dynamic indirection) as follows:
Word 1 - Byte 1 - entity type
- Byte 2 - unit association
Word 2 - Byte 1 - LCN number (0 = local)
- Byte 2 - function set
Word 3 - Byte 1 - data realm
- Byte 2 - revision number
Word 4 - local routing code
4.1.4 Field-Specific Information
POINT NAME—The point name must be from one-to-eight characters long and begin with
"A..Z," "0..9," or "$." Characters within the point name must be "A..Z," "0..9," or "_"
(underscore). Consecutive underscore characters, or trailing underscores are not permitted.
The first trailing "blank" character signals end of the name.
POINT NAME INDEX—Normally will equal zero. This field is not used with user-defined
values; it applies only to certain system data-base points.
PARAMETER—The parameter name must be from one-to-eight characters long and begin
with "A..Z." Characters within the parameter must be "A..Z," "0..9," or "_" (underscore).
Consecutive underscore characters, or trailing underscores are not permitted. The first
trailing "blank" character signals end of the name. See the Computer Gateway Parameter
Reference Dictionary, Hiway Gateway Parameter Reference Dictionary and Network
Gateway Parameter Dictionary for information about TDC 3000
X
standard parameters.