If the device addressed does not understand the control command, the SBI
receiving device continues to operate additionally with a hardware handshake
after it has received another 6 characters.
For data communication with a software handshake, “XON” must be sent
by a device when it is turned on in order to enable another on-line device to
exchange data.
Sequence:
Transmitting device
Receiving device
– – – – – byte – – – –
→
– – – – – byte – – – –
→
– – – – – byte – – – –
→
– –
←
– – – <XOFF> – – – – –
– – – – – byte – – – –
→
(Once <XOFF> has been transmitted, a maximum of
– – – – – byte – – – –
→
14 bytes can still be received.)
:
:
:
Pause
:
:
:
:
:
– –
←
– – – <XON> – – – – – –
– – – – – byte – – – –
→
– – – – – byte – – – –
→
Transmitting device:
The importance of such handshake control for data transmission becomes
especially apparent
– when the continuous automatic data output parameter is defined
– when data output is controlled by application programs.
Once <XOFF> has been received, it prevents further transmission of characters.
When <XON> is received, it re-enables the transmitting device to send data.
The transmitting device is always enabled for sending data after it has been
switched on.
If data transmission is interrupted by the control line (CTS) or the command
<XOFF> while a data block is being output from an application program (only for
printing a section of text with several lines of data), the readout will be locked
into the display at the same time.
Data output will be blocked until the interface receives an enabling signal.
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