Casio CDP-220R - Manual (Page 30)

Session “One session” refers to a series of processes that occur for one user operation. One subsession
or multiple subsessions make up a session. The sender sends EOS (End of Session) to end a session.
Regardless of whether there is a single parameter set or multiple parameter sets being transferred, a bulk
dump always takes the form of a session, never a subsession only.
21.2 One-way Mode Communication Flow
A session starts with the receiving device sending a request using an OBR, or with the sending device
sending OBS data. The session ends after transfer of all the data in the parameter set being transferred
by the sending device is complete.
The transferred messages of a single parameter set cannot exceed 256 bytes. When 256 bytes are
exceeded, data is divided into multiple packets of 256 bytes or less each and transferred at fixed intervals
(20 msec).
A final EOD informs the receiving device when the session is ended.
Data Receiver Data Sender Operation
(External Device) (This Instrument)
OBR -----> Send Request
(Optional)
<----- OBS Data Transfer
(20 msec or greater
interval)
<----- OBS Data Transfer
(20 msec or greater
interval)
<----- OBS Data Transfer
(20 msec or greater
interval)
:
:
<----- EOD End of Data
:
Other Sub Session
:
<----- EOS End of Session
21.3 Handshake Mode Communication Flow
A session starts with the receiving device sending a request using a HBR, or with the sending device
sending HBS data. The sending device does not send the next packet until it receives an ACK from the
receiving device. The maximum wait time of at least 2000 msec is reserved. Failure of a response to
arrive within the wait time is treated as a timeout error, and data communication is terminated. The
receiving devices returns ERR (error) when there is mismatch in the received data checksum or when
an incompatible data format is discovered. When the sending device receives ERR (error) from the
receiving device, it resends the last data sent. If an error repeats a number of times (three times or more
for this Instrument), either the sending device or the receiving device sends an RJC to terminate the
session. A session ends after the sending device transfers the volume of data determined by the number
of parameter sets begin transferred, and sends EOD and EOS in response to an ACK from the sending
device.
30