Diamond Systems JUPITER-MM-SIO Manuel de l'utilisateur - Page 10

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Configuration for RS-422 and RS-485 Modes

When RS-422 or RS-485 modes are selected, not all signals are used by the line drivers and receivers.

Depending on your software configuration, you may need to force some inputs true so that your software will

operate correctly. Jumper blocks J7 and J8 provide a means to force the input signals true (connect them to

ground, or logic 0) for ports 1 and 2, respectively. The signals that can be controlled in this fashion are CTS,

DCD, DSR, and RI. To force an input signal true on a port, install a jumper next to that signal's name on the

corresponding header for that port. Jumpers should not be installed in these locations for RS-232 operation.

NOTE: The positions TX and RX are not used for this purpose. Installing jumpers in these locations has an

entirely different meaning. See Cable Endpoint Termination below.

RS-422 / RS-485 Cable Endpoint Termination

In RS-422 or RS-485 networks, termination resistors are normally installed at the endpoints of the cables to

minimize reflections on the lines. Jupiter-MM-SIO provides 120Ω resistors for this purpose. To enable resistor

termination, install jumpers in the locations TX and RX of J7 or J8 for ports 1 or 2 respectively. Termination is

only needed, and should only be used, at the cable endpoints. Installing termination resistors at additional points

in the network may cause overloading and/or failure of the line drivers.

Interrupt Levels

J10:

J11:

Each serial port requires an interrupt level as well as a base I/O address. Two jumper blocks, J10 and J11, are

provided to select the interrupt level for each port from among levels 9, 3, 4, 5, 6, 7, 10, 11, 12, and 15. Install a

jumper in the position corresponding to the desired interrupt level for each port. A second jumper is usually

required in the R position as well; see "Interrupt Pulldown Resistor" below.

Note: Interrupt levels 3 – 7 and 9 are available on the standard 8-bit PC/104 bus header J1. If you are using an

8-bit bus, these are the only levels available to you. Interrupt levels 10, 11, 12, and 15 are available on the 16-bit

PC/104 bus extension header J2. If you are using a 16-bit bus, then all 10 levels are available to you.

Interrupt Sharing

On the PC/104 bus, a single interrupt level may be shared by multiple devices. A device requesting service

drives the line to a logic high level, and when the device is serviced it tristates the line rather than driving it low.

This technique avoids contention by two devices trying to drive the same line with opposing logic levels.

Jupiter-MM-SIO uses this technique for the two serial ports. To use the same interrupt level for both serial ports,

install a jumper in the same number location for both ports and install a jumper in the R location for only one

port.

Interrupt Pulldown Resistor

In order to guarantee valid logic levels on the line when the device is not requesting service, each active interrupt

level requires a 1KΩ pulldown resistor. Only one such resistor should be used on each active interrupt line. Each

interrupt configuration header on Jupiter-MM-SIO has a position marked "R" for enabling the pulldown resistor.

Install a jumper in this position to connect the resistor, and remove the jumper or install it over 2 pins in the left

column in the header to disconnect the resistor. If two or more ports are sharing the same interrupt level, install

the jumper in the R position for any one of the ports and leave it off the others.

Port 1 interrupt configuration

Port 2 interrupt configuration

Jupiter-MM-SIO User Manual V1.3

p. 10