Casio Personal Computer CTK-900 User Manual

40

A session starts with the receiving device sending a request using an HDR or with the sending device sending 
HDS 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 (at 
least 2000 msec) is treated as a timeout error, and data communication is terminated. 
The sending device resends the last data if the receiving device returns an HDE (error) due to checksum mismatch, 
incompatible data structure, or some other reason. If an error repeats a number of times (undefined), either the 
sending device or the receiving device sends an HDJ to terminate the session. 
A session ends after the sending device sends all the parameter sets, and sends a final EOD in response to an 
HAD (ACK) from the sending device. 

The same packet is resent when a checksum mismatch or incompatible data structure error is detected. 

Data send is canceled when no acknowledgement (ACK) is received. 

Data Receiver

Data Sender

Operation

HDR →

Send Request (Optional)

← HDS

Data Send

HDA →

Acknowledge 

← HDS

Data Send

HDA →

Acknowledge 

:
:

HDA →

Acknowledge 

← EOD

Data End

:

  Other subsessions

:

← EOS

End of session

Data Receiver

Data Sender

Operation

HDR →

Send Request (Optional) 

← HDS

Data Send

HDA →

Acknowledge 

← HDS

Data Send

HDE → Error

← HDS

Data Resend

:
:

HDE →

Error 

← EOD

Data End

:

  Other subsessions

:

← EOS

End of session