CONTENTS
Among medical information systems, clinical laboratory information systems indispensable as a diagnostic aid. To establish the clinical laboratory system, we require an online connection between automated analyzers and computer systems Sometimes, different equipment models have different protocols for connection. Standardization is desirable.
The Japanese Association of Healthcare Information Systems Industry (JAHIS) established the Clinical Laboratory (in hospital) System Special Committee, Analyzer Interface Working Group. This group studied the connection protocols between automated analyzers and computer systems, and established the standard guidelines.
The connection protocol between instruments and computer systems in Japan is the “Bit serial interface standard guideline.” This document was published in 1981 by the Interface Investigation Committee of the Japan Clinical Laboratory Automation Study Group, and was complied with by many manufacturers. This guideline deals with mainly the specifications for electrical and mechanical connections. On the other hand, the protocol for information communication was drafted by each analyzer manufacturer. Different protocols were used for different equipment models, even from the same manufacturer. To solve this problem, standardization of protocols is required not only at the domestic level but also at the international level. The purposes of standardization are to prevent diversification of connection procedures between instruments and computer systems and to improve the reliability of communication data.
To study standardization at the international level, we surveyed the United States ASTM (American Society of Testing and Materials) E1381-91 which details connection protocol and message structure.
ASTM E1381 is “Specifications for low-level protocols for message transmission between clinical laboratory instruments and computer systems.” However, this is not sufficient. Analyzers to be covered by a “new standard guideline” require the immediate responsiveness of computer systems. They handle multiple items. E-1394 transmits and receives information for each layer, thus increasing the number of transmissions and receptions. The measurement result fields for multiple items require further investigation.
The connection protocol between instruments and computer systems shall be defined by standardization of the physical layer and data-link layer (from electrical and mechanical connection specifications to information communication connection procedures). The purposes are to prevent diversification of connection procedures between instruments and computer systems and to improve the reliability of communication data.
1) A standard guideline shall not disturb the progress of the automated system.
2) It shall be applicable not only in Japan but also internationally.
3) In the future, a LAN connection standard guideline shall be drafted. Revision of these guidelines shall be studied when necessary.
Data transmission shall be of start-stop synchronous semi-double type.
Signal levels shall conform to JIS X5101 as follows
|
Control signal |
Input signal level |
Output signal level |
|
1 |
- 3 V or less |
- 5 V to - 15 V |
|
0 |
+ 3 V or more |
+ 5 V to + 15 V |
|
|
Content | |||||
|
Start bit |
1 bit | |||||
|
Data bit |
7 bits |
8 bits | ||||
|
Parity bit |
Even number |
Odd number |
None | |||
|
Stop bit |
1 bit |
2 bits | ||||
|
Communication speed |
1200 bps |
2400 bps |
4800 bps |
9600 bps | ||
Note 1) A start bit is binary 0. A stop bit is binary 1.
Note 2) The values in the shaded boxes shall be standard.
Connector shape and pin position shall be selected from among the following two kinds.
The connector shape shall conform to JIS X5101. Pins on instruments shall be of male type (DB-25P). Pins on connectors shall be of female type (DB-25S).
Pins shall be arranged as follows
|
Pin No. |
Name of signal |
|
Pin No. |
Name of signal |
|
Pin No. |
Name of signal |
|
1 |
Shield |
|
11 |
|
|
21 |
|
|
2 |
Data output |
|
12 |
|
|
22 |
|
|
3 |
Data input |
|
13 |
|
|
23 |
|
|
4 |
|
|
14 |
|
|
24 |
|
|
5 |
|
|
15 |
|
|
25 |
|
|
6 |
|
|
16 |
|
|
|
|
|
7 |
Signal GND |
|
17 |
|
|
|
|
|
8 |
|
|
18 |
|
|
|
|
|
9 |
|
|
19 |
|
|
|
|
|
10 |
|
|
20 |
|
|
|
|
Note 1) Pin No.1 shall be a shield connection which is connected to instrument enclosures.
The shield connection shall be open at the computer to avoid a grounding loop.
The connector shape shall conform to JIS X5103. Pins on instruments shall be of male type (HDEB-9P). Pins on connectors shall be of female type (HDEB-9S).
Pins shall be arranged as follows
|
Pin No. |
Name of signal |
|
1 |
|
|
2 |
Data input |
|
3 |
Data output |
|
4 |
|
|
5 |
Signal GND |
|
6 |
|
|
7 |
|
|
8 |
|
|
9 |
|
Note 1) The case ground is recommended for 9-pin connector shield if necessary.
Character codes shall be as specified by JIS X0201 and JIS X0208.
|
STX |
F# |
Frame message |
ETX or ETB |
CSH |
CSL |
CR |
LF |
|
|
Content | |||
|
Maximum frame length |
247 bytes |
256 bytes |
512 bytes |
1280 bytes |
Note 1) The value in the shaded box shall be standard.
|
Code |
Hexadecimal digit |
Content |
|
STX |
02 |
Start of text (frame) |
|
F# |
Note 1 |
Frame No. |
|
Frame message |
|
Text or text part |
|
ETX |
03 |
End of text (frame) |
|
ETB |
17 |
End of transmission block |
|
CSH |
Note 2 |
Upper digit of check sum |
|
CSL |
Note 2 |
Lower digit of check sum |
|
CR |
0D |
Recovery |
|
LF |
0A |
Start of a new line |
|
Code |
Hexadecimal digit |
Content |
|
ENQ |
05 |
Inquiry (Demand for open station) |
|
ACK |
06 |
Affirmative answer |
|
NAK |
15 |
Negative answer |
|
EOT |
14 |
Transmission end and receiving |
Note 1) Calculation method of frame No.
Note 2) Calculation of check sum
The data link layer establishes the link between instruments and computer systems, transmits and receives data, detects errors, and recovers from errors. The data link layer has 4 phases: Neutral, Established phase, Transfer phase (Receiving phase), and Termination phase. Instruments and computer systems shift synchronously. Shift is started by a procedure (Established phase) which determines the information sending party and the receiving party. Until the next Neutral comes, the receiving party cannot return (send) information, except the receiving protocol.
At each phase, either system (the sending party) instructs an action to maintain communication to ensure functions at the sending party and the receiving party. Usually, a system which has no information monitors the system data link and detects the Established phase. Such a system serves as a subordinate station, and waits for information sent by a main station.
A data link layer has a data transmission system which is called a frame.
It can define the maximum frame length which was determined by instruments
and computer systems. If the message to be sent exceeds the maximum frame
length, it shall be split to be within the maximum frame length, and sent
consecutively twice or more.
It is necessary to prevent deviation of communication phase between instruments and computer systems. Therefore, waiting time is required between the Neutral and the Established phase.
The Established phase determines the data transmission direction, and prepares the receiving party for receiving information.
The party which has information to be sent must confirm the Neutral of lines and inform the other party that transmission will start. For that party, it sends ENQ control characters. The receiving party in Neutral (which has no information to be sent) receives ENQ, responds with ACK control characters, and informs that Receiving phase is ready. Other characters are all neglected. When the ENQ sending station receives ACK, the main station (sending party) and subordinate station (receiving party) will be established. The Established phase will end and it will shift into the Transfer phase. (When the Established phase ends, the sending party is the main station and the receiving party is the subordinate station.)
If the ENQ receiving party cannot be ready for receiving information, it responds with NAK transfer characters. When the sending party receives NAK, it must be Neutral for at least 10 seconds until it sends the next ENQ (Setting of stand-by time).
When both parties send ENQ at the same time, data link computer systems. If such a situation occurs, instruments always have priority in sending information. Solutions are as follows.
a) Computer systems
If computer systems send ENQ transfer control characters and receive ENQ, they must stop transmission and be ready for receiving information. They must be Neutral for 20 seconds, receive ENQ from instruments and respond with ACK or NAK, the phase of receiving preparation.
b) Instruments
If instruments send ENQ transfer control characters and receive ENQ, they must be Neutral for at least 1 second before they send the next ENQ.
When ENQ is sent, a timer is set. If ACK, NAK, or ENQ is not received, the time is over and it shifts to the Termination phase.
During the Transfer phase, the main station sends information to the subordinate station. This phase continues until all information has been sent out.
Information is sent by frame. Information having different purposes cannot be placed in a single frame. The frame length must be within the preset maximum length of frame. If the information exceeds the maximum frame length, it will be split into two or more frames.
There are two types of frame; a middle frame and an end frame. The middle frame end with ETB, checksum, CR, and LF. The end frame ends with character ETX, checksum, CR, and LF. The middle frame is used to send information that is longer than the maximum frame length. If the information is within the maximum frame length, it is sent by the end frame.
After sending a frame, the main station does not send any more frames until a response is received.
The receipt of an ACK response indicates that the information was received correctly up to the end of the frame and that the subordinate station is ready to receive the next frame. The main station increments the frame number and sends a new frame, or shifts to the Termination phase.
The receipt of a NAK response indicates that the information was not received correctly and that the subordinate station is ready to receive the same frame again.
The receipt of an EOT response indicates that the information was received correctly up to the end of the frame and that the subordinate station is ready to receive the next frame. However, this response is also a request from the subordinate station for the main station to stop transmission of information as soon as possible.
If an EOT response is received instead of the usual ACK response during the Transfer phase, the main station must interpret this response to be a request from the subordinate station to stop transmission. EOT is a positive, affirmative response indicating that the end of the frame has been received. It indicates that the subordinate station is ready to receive the next frame. At the same time, however, it is a request for transmission to be stopped.
After the main station receives a request from the subordinate station for transmission to be stopped, it is preferable for the main station to stop transmission. If the main station ignores the EOT response, the subordinate station must repeat its request for stoppage of transmission in order to make the request effective.
When the main station accepts a request for stoppage of transmission from the subordinate station, it is necessary for the main station to enter the Termination phase and return the data link to the Neutral. A subordinate station can then enter the Established phase and become a sending party. The original sending party cannot enter the Established phase until at least 15 seconds have elapsed or until the original receiving party sends information and returns the data link to the Neutral.
In the Termination phase, the data link returns to the Neutral.
When all information has been transferred , the main station sends EOT to the subordinate station.
The main station sends EOT transfer control characters and then assumes that the data link is in the Neutral.
The main station and subordinate station must recover from errors appropriately as follows.
The subordinate station inspects all the frames and verifies their validity. For an invalid frame, it sends a NAK response. When the main station receives a NAK response, it sends the last frame again retaining the same frame number. Thus, transmission errors are detected and corrected automatically.
When the subordinate station inspects frames, it neglects all the characters before STX, or all the characters after the block end characters (ETB or ETX). Frames are valid when they meet all the following requirements:
a) Character errors must not be detected (parity error, framing error, etc.)
b) The frame checksum must agree with the checksum that was calculated based on the received frame.
c) The frame number must equal to that of the last received frame or must be larger by one.
When a NAK response or a response other than ACK or EOT is received (NAK status), the main station increments the retransmission counter and retransmits the frame. If an independent frame is sent, and the retransmission counter indicates that transmission has failed 6 times, then the main station must shift to the Termination phase and interrupt this transmission. This enables the main station to escape from the phase in which transmission cannot be continued.
A time-out is used to detect failure of adjustment between the main station and the subordinate station. The time-out is also used as a recovery tool when communication lines or other equipment fail to respond.
During the Established phase, the main station sets the time-out when it sends ENQ. If ACK, NAK or ENQ is not received within the 15-second time-out period, the main station enters the Termination phase.
When contention is detected during the Established phase, the time-out is set by the party that detected contention (receiving party). If ENQ is not received within the 20-second time-out period, the receiving party assumes that the lines are in the Neutral.
During the Transfer phase, the main station sets the time when it transfer the last character of frame. If a response is not received within the 15-second time-out period, the main station enters the Termination phase and interrupts the transmission of information. When defective frames are transferred several times, the information to be sent must be kept in the memory to ensure complete repetition.
During the Transfer phase, the subordinate station enters the Transfer phase first or sets the time when it responds to a frame. If a frame or EOT is not received within the 30-second time-out period, the subordinate station discards incomplete information to be sent and assumes that the lines are in the Neutral.
If the subordinate station does not respond to a frame within 15 seconds, a time-out occurs at the main station. If the subordinate station cannot respond because of frame handling or other reasons, and if the response time is longer than 15 seconds, the information to be sent is interrupted by the main station.
Clinical laboratory instrument that analyzer specimen automatically.
Addition data used for the detection of data errors.
The second layer of the seven-layered open systems interconnection (OSI)
communication protocol. Used to send or receive text as a frame. Performs
link connection and release, sending structure creation, sequence control,
error detection and recovery etc. This layer controls the transfer software.
Components of the text, such as the specimen number field or name field.
A message segment. It is used for error checking, affirmative responses,
and other periodic communication monitoring.
The section of the frame that contains the text. The frame number is also
indicated in this section when the text exceeds the maximum frame length.
Data sending party in Transfer phase.
A collection of related information concerning a single item.
Rest phase in which information is neither transmitted nor received. Immediate
shifting to the Established phase or the Receiving phase is possible.
Additional bit for odd number/even number test.
The first layer of the seven-layered open systems interconnection (OSI)
communication protocol. It sets or releases the electrical/mechanical status
of communication lines.
Total communication activity.
Chinese character code system mainly used for personal computer systems.
In shift JIS, 2 bytes represent one character. However, the first byte
is assigned to an area which is not used by ANK. Thus Chinese characters
and ANK are differentiated.
Data receiving party in Transfer phase.
Same as the text of the Bit Serial Interface Standard Guidelines of the
Japan Clinical Laboratory Automation Study Group. It can be a measurement
result text or request information text. It is defined by the text format
for each equipment.