Casio CTK-4200 manual 31

Data Receiver		Data Sender	Operation
(External Device)		(This Instrument)
HBR	----->		Send Request
			(Optional)
	<-----	HBS	Data Send
ACK	----->		Acknowledge
	<-----	HBS	Data Send
ACK	----->		Acknowledge
	:
	:
ACK	----->		Acknowledge
	<-----	EOD	End of Data
	:
	Other Sub Session
	:
	<-----	EOS	End of Session

The packed with the same packet number is resent when a checksum mismatch or incompatible data format error is detected.

Data Receiver		Data Sender		Operation
(External Device)		(This Instrument)
HBR	----->			Send Request
				(Optional)
	<-----	HBS		Data Send
ACK	----->			Acknowledge
	<-----	HBS		Data Send 1
ERR	----->			Error
	<-----	HBS		Data Send 2 (Retry
			1)
ERR	----->			Error
	<-----	HBS		Data Send 3 (Retry
			2)
ACK	----->			Acknowledge
	:
	:
ACK	----->			Acknowledge
	<-----	EOD		End of Data
	:
	Other Sub Session
	:
	<-----	EOS		End of Session

Session terminates if ERR is detected a number of times.

31