Hitachi PH Instruction Manual page 178

(8) Up to 1500 bytes of data can be transmitted at a time, including
"STX" and "ETX". If the 1500-byte limit is exceeded,
a communication error (NAK response) occurs.
(9) Any data transmitted by communication (print contents, print
specifications, print format, and user pattern) is not stored
except in the following cases.
[Conditions for storing the data]
When the ink is stopped after communication by the Shut down key or a stop
1
signal.
2 When switched from another screen to the print description screen by operating
the touch panel.
3
At 01 minute of every hour.
(10) Communication when "ENQ" is omitted is also possible.
1 When ENQ and ACK are present:
External device
ENQ
IJ printer
2
When ENQ is omitted:
External device
IJ printer
STX Text
ACK
STX Text
EXT
ACK
EXT
ACK
● Transmission Sequences 6-17