Data Transmission Control Procedure; Establishment Of Data Link; Response To Information - Hitachi 902 Service Manual

16.4 Data Transmission Control Procedure

16.4.1 Establishment of Data Link

(1) Upon input of [YES] for host communication on the start condition screen, the analyzer
side transfers ANY frame to the host. This marks the start of communication.
(2) Once a text has been sent, the direction of transmission is reversed and the receiver can
send the next response or text. In subsequent steps, the analyzer and host continue
transmission alternately.

16.4.2 Response to Information

(1) Upon receiving information, the receiver sends a response or text (see Table 16-4) to
inform the sender of the receiver status and the validity of received information.
(2) Used for response is a text in which a character identifying its purpose (frame character) is
put between STX and ETX. When the 256-byte mode is selected for the transferred byte
count, the analytical data text may exceed 256 bytes (including STX and end-of-data
code) depending on sample. In this case, the text is analyzed, the analyzed text is put
between STX and ETX and a frame character to identify the number of transmissions is
added in the text.
(3) After sending a text, sending should be avoided until reception of a response or request
to/for the text in a normal condition. If sending is attempted, the analyzer side ignores it.
(Trace will not be made either.)
If no response is returned or an invalid response is received, the recovery procedure is
executed. In case of sending from the host, it must always be kept ready for receiving.
(4) If the host did not return a response in the communication cycle (NOTE) on
communication from the analyzer, alarm is displayed on the screen of analyzer.
NOTE: Time period is changeable on the communication parameter screen. It is defaulted to
2 sec.
Communication cycle
T
Analyzer
HOST
Conversation
T: Text (contents of message)
Transfer sequence
T T
T
T
Cluster
16 - 9