Siemens SIMATIC TIWAY 1 - Manual (Page 179)

USING THE NON-INTELLIGENT TERMINAL PROTOCOL
UNILINK HOST ADAPTER A–3
USER MANUAL
A.1.2 Message Delimiters
A colon ( : ) marks the beginning of a message and a semicolon ( ; ) marks the end
of a message. Any characters between a colon and the next semicolon are
interpreted as a valid message, while any characters between a semicolon and
the next colon are ignored. This allows the host to use any parameters required
by its software between lines of output. When transmitting data to the host, the
UNILINK Host Adapter sends carriage return and line feed characters after
the terminating semicolon, to scroll the response on ASCII terminals. More
intelligent host devices can be set to filter out the carriage return and line feed.
A.1.3 Character Count
To aid in error control, the colon at the beginning of the message is followed by a
four-character count field representing the total number of printable
characters in the message, including the colon, character count, message body,
error checking code, and the terminating semicolon. The four characters
represent a 16-bit hexadecimal value such that a count of 100 characters will be
represented as 30 30 36 34 (0064 hex). NITP messages are limited to a maximum
length of 590 characters.
A.1.4 Message Body
The message body consists of ASCII character pairs, from the character set in
Table A–1, representing a single binary byte value. The binary values from each
character pair is the adapter command string discussed in Chapter 2 and
Chapter 5. The maximum message body length is 580 characters.