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Command and Response Formats
Section 6-4
FCS, Terminator
Refer to the corresponding explanations under “Command Format.”
Long Transmissions
The largest block of data that can be transmitted as a single frame is 131
characters. A command or response of 132 characters or more must there-
fore be divided into more than one frame before transmission. When a trans-
mission is split, the ends of the first and intermediate frames are marked by a
delimiter instead of a terminator.
Dividing Commands (Host Computer to PC)
As each frame is transmitted by the host computer, the computer waits for the
delimiter to be transmitted from the PC. After the delimiter has been transmit-
ted, the next frame will then be sent. This procedure is repeated until the
entire command has been transmitted.
Dividing Responses (PC to Host Computer)
As each frame is received by the host computer, a delimiter is transmitted to
the PC. After the delimiter has been transmitted, the PC will transmit the next
frame. This procedure is repeated until the entire response has been transmit-
ted.
Delimiter
Text
Unit No.
Header code
FCS
Delimiter
Frame 1 (command)
Text
FCS
Delimiter
Terminator
FCS
Text
End code
Header code
Unit No.
Frame 2 (command)
Frame (response)
Delimiter
Text
FCS
Terminator
Frame 3 (command)
Host
computer
PC
Delimiter
Text
Unit No.
Header code
FCS
Terminator
Frame (command)
Host
computer
PC
Delimiter
FCS
Text
End code
Header code
Unit No.
Frame 1 (response)
Text
FCS
Delimiter
Frame 2 (response)
Delimiter
Text
FCS
Terminator
Frame 3 (response)
