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1.3) Differential/Single-ended External Interrupt Jumper Setting
Each of the Input lines may be configured for differential of single-ended mode. In
differential mode, each bit of two input lines has an input line and a corresponding return
line. In single-ended mode, the return lines are connected to a single common return line
on the DB37 connector. They are COMA (pin 17) for the Returns of Opto-isolator 0 to 7
and COMB (Pin 36) for the Returns of Opto-Isolator 8 to 15. Differential mode is useful
where inputs of opposite polarity are to be sampled.
The optically isolated input lines can be connected differentially or single ended. Figure
1.5 illustrates this graphically:
Jumper JP3 - A0 is shorted to COMA, it simply shorts the Optically Isolated Line Return
to COMA on the DB37 Connector. You can connect COMA (or COMB) to Digital
Ground (Pin 37) if you want to ground the Return Lines.
Figure 1.5a: Optically Isolated Input Diff/Single-ended Jumper Setting
