Compaq AlphaServer ES45 Service Manual page 235

Through Mode
Through mode is the default operating mode. The RMC routes every character
of data between the internal system COM1 port and the active external port,
either the local COM1 serial port (MMJ) or the 9-pin modem port. If a modem
is connected, the data goes to the modem. The RMC filters the data for a
specific escape sequence. If it detects the escape sequence, it connects to the
RMC CLI.
Figure 7–1 illustrates the data flow in Through mode. The internal system
COM1 port is connected to one port of the DUART chip, and the other port is
connected to a 9-pin external modem port, providing full modem controls. The
DUART is controlled by the RMC microprocessor, which moves characters
between the two UART ports. The local MMJ port is always connected to the
internal UART of the microprocessor. The escape sequence signals the RMC to
connect to the CLI. Data issued from the CLI is transmitted between the RMC
microprocessor and the active port that connects to the RMC CLI.
NOTE: The internal system COM1 port should not be confused with the
external COM1 serial port on the back of the system. The internal
COM1 port is used by the system software to send data either to the
COM1 port on the system or to the RMC modem port if a modem is
connected.
Local Mode
You can set a Local mode in which only the local channel can communicate with
the system COM1 port. In Local mode the modem is prevented from sending
characters to the system COM1 port, but you can still connect to the RMC CLI
from the modem.
Using the Remote Management Console 7-5