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45
Opening a Communications Port
Section 4-2
4-2-2 OPEN Command Specifications
The following details are specified in the OPEN command.
Item Settings Detail
Device symbol (periph-
eral device name) SCRN, LPRT,
EKPRT, NKPRT,
KYBD, COMU,
TERM • Use of the transmission/receive buffer.
• Control of the transmission control signals.
Baud rate 300/600/1,200/2,400/4,800/9,600/19,200/38,400 bps (default: 9,600 bps )
(port 3
≤
19,200 bps)
Data length 7 or 8 bits (default: 8 bits)
Parity None, odd, or even (default: none)
Stop bits 1 or 2 bits (default: 2 bits).
RS-232C port
transmission
controls CTS CTS_ON Executes RTS/CTS flow control for the receive buffer of the external device.
The ASCII Unit monitors the CTS signal during execution of the PRINT
command. When the CTS signal is OFF, data transmission is suspended.
When the CTS signal is ON, data transmission continues.
CTS_OFF RTS/CTS flow control is not executed. The ASCII Unit does not monitor the
CTS signal during execution of the PRINT command.
RTS RTS_ON Turns ON the RTS signal from the opening of the communications port until
it closes. When receiving data normally from the external device into the
receive buffer, RTS must be set to RTS_ON.
RTS_OFF Turns ON the RTS signal only during the execution of I/O commands
(PRINT and INPUT), turning it OFF at all other times. BASIC’s RTS control
is disabled.
RS-232C port
transmission
controls DSR DSR_ON When output commands (such as PRINT or LPRINT) are being executed,
the ASCII Unit checks the DSR signal, and sends data if the DSR signal is
ON. If the DSR signal is OFF, the ASCII Unit waits to transmit until the DSR
signal turns ON. The BASIC indicator will flash slowly while the Unit is wait-
ing to transmit.
DSR_OFF The ASCII Unit does not check the DSR signal when output commands are
being executed.
RS-422A/485 port trans-
mission controls CTS, RTS, DSR
not used
(invalid) ---
Xon/Xoff
(Not available for port 2 of
ASC21.)
XN_ON Controls Xon/Xoff flow to both the ASCII Unit’s receive buffer and the exter-
nal device’s receive buffer.
• ASCII Unit’s Receive Buffer
When the receive buffer of the ASCII Unit reaches 3/4th full (384 bytes), it
sends an Xoff signal, requesting the external device to suspend data
transmission. Once the Unit’s receive buffer drops to 1/4th full (128 bytes),
it sends an Xon signal, requesting the external device to resume data
transmission.
• External Device’s Receive Buffer
When the ASCII Unit receives an Xoff signal from the external device dur-
ing execution of a PRINT command, it suspends data transmission. When
it receives an Xon signal from the external device, it resumes data trans-
mission.
XN_OFF Xon/Xoff flow control disabled.