Schematics EL-3034 through EL-3039 show the layout for one each of the Opto-22 relay racks used in the instrument electronics. The sheets have a block in the upper left-hand area that associates a channel number and a bit number with a function. The channel number gives the location of the I/O module on the individual rack. The bit number gives the I/O bit that the software can read or write and the function tells what the bit toggles or reads.

In the lower left area is a pictorial representation of the actual I/O rack. The drawing shows where the relays are and what their function is. It also tells what relay should be plugged into each slot. Notice that between each relay and its screw terminal is noted what color relay should be installed. The other important piece of information shown here is the position of the various bus bars. These are Sheet metal strips that are used to connect from two to eight terminals together.

On the right-hand side of the drawing is a table showing the destination or the output connections of the I/O relays. The first column gives the I/O bit for programming. The pin column refers to the screw terminals on the edges of the relay racks. The next three columns give the connector and pin numbers that the output is connected to. The sixth column tells what relay part number populates each position on the relay rack. The last column tells the function that the relay controls. On the right-hand side of the table are the channel numbers as labeled on the board.