Euresys Coaxlink 1629, Hardware Manual

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73
If maximizing the opto-coupler switching time is a concern, it is not recommended to not
increase too much the value of the resistor. The opto-coupler circuit behaves better (switching
times) with a load of about 10 mA or higher. R = 180 ohm loads the opto-coupler at 13 mA (3.3
V) and 23 mA (5 V).
Using Local 12 V Power
The power supply voltage is taken from the I/O connector itself, using the power supply pin
“+12V”.
This circuit needs two resistors, named R and R
POL
.
A resistor of 180 ohm 1/8 W is suggested for R, as best compromise but the circuit can also work
within a large range of resistor values from 50 ohm 1/2 W to 10K ohm 1/16 W (1).
A resistor of 560 ohm 1/4 W is suggested for R
POL
, as best companion of R = 180 ohm but the
value of R
POL
can be adapted to match accordingly others R values.
If an existing pull-down resistor is already available at the TTL receiver side it can be used as R
resistor to operate the circuit, avoiding the need of adding an extra resistor somewhere in the
cabling.
The circuit does not perform logic level inversion.
TIP
The resistor value can be also changed to match special static or dynamic
performance requirements.
NOTE
The circuit does not perform logic level inversion.
Coaxlink Hardware Manual