Owner`s manual
17
In Mode of Operation 1, the Model 24H will provide full duplex
communication between the host port and the selected peripheral port.
Port 2 is the selected peripheral port when the Model 24H powers up.
The host port and the selected peripheral port will remain connected
until a different peripheral port is selected. This is accomplished by
sending a port select sequence. Data received by non-selected
peripheral devices will be stored in the Model 24H's buffer and then
sent to the host device when the peripheral port is selected.
When switching between peripheral ports, there may be some question
as to which is the last character received from the current port and
which is the first character received from the new port. To avoid this
potential confusion, it is recommended that you use the following port
selection example when selecting a different port for communication.
Suppose you are transmitting and receiving data from Port 2 and you
wish to switch to Port 3. Use the following procedure:
1. Send $SELECT and nothing else.
2. Wait for at least one and one-half character times of the host
port, but no longer than ten seconds (see NOTE below).
3. Check the receive buffer of the host device for any characters
from the currently selected peripheral port while delaying. If no
character(s) are in the host device's receive buffer send 03
followed by
Carriage Return
or
Line Feed
to select Port 3. If
there are characters in the host's receive buffer repeat step 2
before sending 03 and the terminating character. The Model
24H does not start loading data from the new peripheral port into
the host port until the new peripheral port number and
terminating character are received.
NOTE: The port select sequence has a ten second timer. The timer
starts when the first character of the port select sequence is received.
Any incomplete sequence received ten seconds or more after the first
character has been received will be treated as normal data and will be
sent to the current selected peripheral port.