Appendix E
OsmoTECH XT LIS Specification
85
OsmoTECH XT Single-Sample Micro-Osmometer User Guide
Transfer phase:
In transfer phase, the sender transmits
messages to the receiver in frames. Each frame contains
a maximum of 64,000 characters including frame
overhead.
Although the LIS01-A2 standard states long messages
can be sent by being broken up into multiple frames, the
instrument software is not currently configured to handle
this situation. A frame starts with the
<STX>
character
(ASCII decimal 2), followed by a frame number which is a
single digit from 0 to 7. The first frame in a transfer
begins with frame number 1 and is incremented for each
successive frame until it reaches 7. After frame 7, the next
frame is given a number of 0, and continues to increment
as above.
The frame number is used to distinguish between new
and re-transmitted frames. The message part is
terminated with the
<ETX>
character (ASCII decimal 3),
followed by the checksum (see below) and
<CR><LF>
.
Checksum:
The checksum indicates if a frame is
defective. It is encoded as two ASCII characters and is
computed by adding the ASCII decimal values of all the
characters in the frame starting with the frame number
and ending with the
<ETX>
character. Only the least
significant 8 bits are kept and are converted to
hexadecimal digits making up the two ASCII characters.
Acknowledgment:
The sender waits for an
acknowledgment from the receiver after each frame is
sent. There is a timeout of 15 seconds upon receiving the
acknowledgment.
•
If a timeout occurs, the termination phase begins for
the instrument, and the entire message is re-queued
for transmission.
•
If a reply of
<ACK>
is received, the transmission was
successful and a new frame can be sent.
•
If a reply of
<NAK>
is received, there was an error
during transmission or in the checksum calculation.
The frame should be retransmitted within six retries. If
the limit of six is reached, the message should be
re-queued for transmission.
•
If a reply of
<EOT>
(ASCII decimal 4) is received, the
receiver requests termination of the transmission. In
the instrument, this causes the transmission to end
and the message is re-queued as above.
Termination phase:
The sender transmits an
<EOT>
character to indicate all frames have been sent. Both the
sender and the receiver consider the link to be in the
neutral state after the exchange of the
<EOT>
character.
E.5 Message layer
The message layer describes content of messages based
on the LIS2-A2 standard. Any restrictions and
exemptions will be noted when applicable.
Message content
The following limitations and specifications apply to the
message content:
•
Allowed characters are in single byte, eight bit values
(Latin-1 character set) in the decimal ranges of
32 to 126 and 128 to 254, plus decimal values 7, 9, 11, 12,
and 13. Some fields may be UTF8-encoded as
indicated.
•
The maximum field length within a record is noted in
the detailed specification.
•
The instrument as a sender always uses the following
suggested delimiters:
–
ӏ
as
field delimiter
–
\
as
repeat delimiter
–
^
as component delimiter
–
&
as
escape character
•
The instrument as a receiver handles any other valid
set of delimiters (see LIS2-A2 section 5.4).
•
The instrument does not transmit
null
values to
indicate that the value has not changed since the last
transmission, and does not use received
null
values.
•
Any received fields not required by the instrument are
ignored and are not covered in this guide.
•
The following record types are not sent by the
instrument and are ignored if received:
–
Comment
(C)
–
Scientific
(S)
–
Information
(M)
•
All date/time fields are specified as
YYYYMMDDHHMMSS
where
HH
is a 24-hour time.
•
Universal test ID fields indicate the test type or the
quality control type.
