Dec 15

Some IO pins on the FB have separate pins for input and output. For example, input 1 on port G is available on pin J6.24 while the output 1 of port G is available on pin J6.23. On most controllers all pins are bi-directional, outputs are internally fed back to the input buffer so when you set an output and read the port status it shows the current output state.

On the FB this seems to be different for certain pins, to verify if indeed there is no internal feedback line a small test setup is made. A 220E resistor is connected to J6.40 (Vdd) and to the anode (+) of a low current LED. The cathode (-) is connected to J6.23 (OG1). The LED lights up, so this means the output is low. A separate wire is connected to J6.1 (Gnd) and so far not connected on the other side. This will be uses to apply a low level to J6.24 (IG1).

Using a SSH terminal to the FB, type the command setbits -p g -b 1 -s 1, this will set bit 1 on port g to a high level and the LED will switch off. Using setbits -p g -b 1 -s 0 the low level is put back and the LED will light again.

The command readbits will display a bit pattern of all the available ports a, b and g. The most right one using 32 bits is of port g, MSB on the left, LSB on the right. The 2nd most right indicates the state of IG1, with the wire disconnected this is a high level. When inserting the wire into J6.24 and repeating the readbits command indeed the level is now 0.

The final test is simple (but almost no longer needed), set OG1 to 1 and keep the wire inserted. The LED will switch off, using the readbits command will still show IG1 is 0. Conclusion, no internal feedback so the suggested use for the interface between the FB and the primary motor cortex is possible.

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