The DIVO board has two General Purpose Interface (GPI) connectors, each associated with one of the serial digital video ports. (two transmit and two receive channels each). Figure A-1 points out the General Purpose Interface (GPI) connectors on the DIVO panel.

Figure A-2 shows pinouts for the GPI; the information is applicable for both the IN GPI and OUT GPI connectors.

Each +/- signal pair of the same name applies to one channel of either a receive or transmit optical device. Table A-5 gives the meaning of the pins in Figure A-2.

Figure A-3 shows the location of the jumper pins on the board.

Note that the jumpers for the OUT GPI connector are near the OUT GPI mini-DIN connector, the jumpers for the IN GPI connector are far away from the IN GPI connector.

Each GPI header (row of four pins) configures one of four receiver channels: two channels for GPI in and two channels for GPI out. For the factory setting of switch closure mode, two jumpers are factory-installed, shorting pins 1-2 and pins 3-4. These jumpers need not be moved unless you wish to use current sense mode. You can choose to mix the modes for the various channels. This reconfiguration is typically performed by a Silicon Graphics System Service Engineer when the DIVO board is installed in the chassis.

Figure A-4 shows GPI headers and jumpering. The printed circuit board (PCB) reference designators are included to aid identification of the header associated with each GPI receiver channel.

GPI Contact Closure Transmit (CCT) outputs use an optically coupled solid-state array (SSR) to provide a means of electrical isolation for destination equipment. The GPI transmitter is triggered by a computer command which forward-biases the internal LED, which in turn drives the output MOSFET, closing the contacts of the SSR.

When the GPI trigger is off, a high resistance exists between the CCT+/- terminals. When the GPI is on (triggered by the computer), a low resistance exists between the terminals.

Figure A-5 and Table A-6 show electrical specifications for the GPI transmitter.

The GPI transmitter can be interfaced to the destination equipment by tying the CCT- terminal to GND and using the CCT+ terminal as a current sink. The input device can consist of a logic device with active pullup, an optoisolator LED with series-limiting resistor, or relay primary with series-limiting resistor.

The GPI transmitter's logic sense can be swapped (inverted) by tying the CCT+ terminal to the logic power supply (VCC) of the destination equipment and using the CCT- terminal to drive the input of the receiving device.

GPI Contact Closure Receive (CCR) inputs use a optical isolator device to provide a means of electrical isolation from source equipment. The device consists of a bidirectional input LED optically coupled to a bipolar transistor. A voltage pulse applied across the CCR+/- pins causes the LED to become forward-biased and to produce a GPI trigger to the computer.

Table A-7 summarizes electrical specifications for the GPI receiver optoisolator.

For current sense mode, the CCR+ and CCR- signals can be interfaced by tying the CCR+ terminal to the output of a TTL or CMOS logic device, and by tying the CCR- terminal to GND of the source equipment. Whenever the logic device is driving a logic high, a GPI trigger is generated.

In current sense mode, the logic sense can be swapped (inverted) by moving the CCR- signal from GND to the logic power supply (typically VCC) of the source equipment. The CCR+ signal remains connected to the output of the logic device; however, in this configuration an open collector type device can be used. Whenever the logic device is sinking current a logic low, a GPI trigger is generated.