Black Box RS-485 Manual De Usuario

Set jumpers to “N” for single interrupt mode. This setting is the normal
setting for most applications.

Set jumpers to “S” for shared interrupt mode for all ports sharing an IRQ
except one. Set that port block for “M.” This provides the pull-down resistor
circuit that makes sharing of IRQ’s possible. If you are using more than one Dual
Port RS-232/422/485 Serial Interface or a compatible card in a bus, you should only
have one port set to “M.”

Set jumpers to “S” if you are using more than one Dual Port 
RS-232/422/485 in a bus or if you wish to completely remove the pull-down
resistor for hardware compatibility. Setting the board in this configuration
when it is not accompanied by a pull-down resistor will prevent the ports from
triggering an interrupt.

To select the RS-232 mode of operation, install DIP shunts in the sockets
found at E5 and E8. E5 sets Port 1 and E8 sets Port 2. These DIP shunts are
completely independent of each other, allowing the user to select a single-
port RS-232 or a single-port RS-422.

There are no modem control options for the RS-232 interface: all control
signals are implemented. If your software requires certain handshaking
signals to be active, then you must connect them either to the device with
which you are communicating or you can satisfy the handshake signal
requirements by connecting pins 7 to 8 (RTS to CTS) and pins 4 to 6 to 1
(DTR to DSR & DCD). Make these connections on the DB9 connector that
connects to each port. Refer to Figure 4-3 when making these connections.
(The table on page 4 lists the RS-232 pinout descriptions.)