Chapter 5. Rs-232 Protocol - Sharp ER-A440 Service Manual

CHAPTER 5. RS-232 PROTOCOL

1. Basic protocol specification
1) Data transmission from the host to a satellite
( 1 ) Inquines of the satellite.
( 4 ) Receives ACK.
( 5 ) Sends the text.block.
Start code
( 7 ) Resends the text block if NAK is received.
Resends the text block up to two times.
Sends EOT and terminates the operation
with error if NAK is still received after the
second resending of text block.
( 9 ) Sends the next text if ACK is received and
sends EOT and waits for ENQ.
Dummy Terminal No.
(3bytes) (6bytes)
Text (parameter)
Text (DATA)
Host Satellite
ENQ
ACK
End code
NAK
ACK
EOT
ENQ
ACK
Continued on the
next page
– 4 –
( 2 ) Receives ENQ.
Checks the terminal No.
to see if it is its own.
( 3 ) Sends ACK.
( 6 ) Receives text.
Checks the check sum,text
data,etc. And goes to (8)
if there is no error in them.
( 8 )' Sends NAK if any error
occurs.
( 8 ) Sends ACK.
( 10 ) Terminates the operation if EOT
is received.