User Manual

Operation
RFI-9256 Radio Modem User Manual Page 15 of 96
4.1.2 Control Lines and Flow Control
The main serial port has four control lines:
 Ready to Send (RTS)
 Clear to Send (CTS)
 Data Terminal Ready (DTR)
 Data Carrier Detect (DCD)
The main serial port supports hardware flow control using the RTS and CTS control lines. When hardware
flow control is enabled:
 The radio will only transmit data to the DTE when the RTS line is high.
 The radio will raise the CTS line when there its input buffer is less than the high water mark
(defaults to three quarters full), and drop the CTS line when its input buffer is greater than or equal
to the high water mark.
The flow control high water mark can be configured by the user.
In addition to hardware flow control, the CTS and DCD lines can be configured to behave in one of the
following ways:
 ONLINE controls CTS/DCD: The line is active when the front panel online LED is green or red,
and is off when the front panel online LED is black.
 NEWTORK LINK controls CTS/DCD: The line is active when the front panel network link
LED is green or red, and is inactive when the front panel online LED is black.
 CARRIER DETECT controls CTS/DCD: The line is active when the front panel carrier detect
LED is green or red, and is inactive when the front panel online LED is black.
 Remote DTR controls CTS/DCD: The line is active when a remote radio’s DTR input line is
active in point-to-point or Hayes dial-up mode.
 Local DTR controls CTS/DCD: The line is active when the local radio’s DTR input line is
active.
 Remote RTS controls CTS/DCD: The line is active when a remote radio’s RTS input line is
active in point-to-point or Hayes dial-up mode.
 Local RTS controls CTS/DCD: The line is active when the local radio’s RTS input line is active.
 CTS/DCD Always ON: The line is always active.
 CTS/DCD Always OFF: The line is always inactive.