Star Micronics SP300 Series - Manual (Page 23)

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2-6-3. STX-ETX mode
This mode is accessed from whichever DTR mode or X-ON/X-OFF mode.
To set this mode, the data buffer must be empty.
The host computer sends an ENQ code to the printer and acknowledges the printer
status. Then, the host computer checks if the printer buffer is empty. After the host
computer detects that the buffer is empty, a STX code and data are transmitted.
After 1 block of data is transmitted, the host computer sends an ENQ code to the
printer and then receives the printer status and check byte (horizontal parity for
the printer.)
At this points, the host computer performs a status and horizontal parity check.
When the host computer determines that there was no error, it transmits an ETX
code which serves as text end code. After the printer receives the ETX code, data
in the data buffer is printed out. If an error occurs, a CAN code is transmitted by
the host computer. (In this instance, the data which was previously sent to the
buffer is cleared, thus, the host computer must retransmit the same data to the
printer.)
A flowchart of this operation is illustrated on the following page.
[Status]
[Framing error]
A framing error occurs when SPACE is detected at the stop bit. When a framing
error or a vertical parity error occurs for the data which is received, the printer
prints out a “?” mark to indicate that the error occurred.
Mechanical error
1: error
Buffer empty
1: empty
Buffer overflow
1: overflow
Compulsion switch
High level
(Switch is set to ON)
b7 b6 b5 b4 b3 b2 b1 b0
Constantly
set at “0”
Vertical parity error
1: error
Framing error
1: error
Paper empty
1: empty
0