I have a setup running (currently) one Tic Controller using serial transmission. I have a Raspi 3+ running Python and everything is working fine. I went the serial route, instead of i2c, because I have to transmit the commands a bit further than is suggested for i2c.
I am running at 9600 baud, but have also tested 115K without issues.
As indicated in the Tic manual, I will need an AND gate to get reliable communication from multiple Tic controllers. I know there are many logic chips available, but as a general guide, is there a suggested chip, or operational specs. one should use for selection?
Furthermore, can the AND Gate chips be cascaded?, i.e. I see some chips with 4 inputs and one output that run in the 3-5V VCC range. TI has a chip (SN54HC21)that is in a DIP pkg, so I can easily breadboard it. Since I am looking at controlling 24 stepper motors, it would seems I would need to have 6 chips (6 x 4 = 24) outputting into a set of two chips which then feed a third chip to get the 24 signals down to one going into the Raspi. I think looking at the datasheet for the chip, I may need to hold the unused 4th input HI on the second set of two chips.
I’m not looking for anyone to do the work for me, so to speak, just wanted to make sure I am not going down an incorrect path. This is not my area of expertise.
As you mentioned, there are many AND gate chips available; as long as they operate in the correct voltage range, it should generally be fine. The SN54HC21 chip you mentioned from TI would be a viable option.
Yes, you can cascade AND gates to get the number of inputs you need back down to one return signal, so it sounds like you are on the right track.
I received the TI chips (SN54HC21) and went about doing a quick breadboard as a sanity check. In the final application, the serial communication will be between the Tic controlllers and a RPi, the serial signals get level shifted down to 3.3V just before going into the RPi’s serial pins.
In order to quickly test the behavior at 5V, I set up an Arduino to put out a signal on it’s serial pins. I didn’t realize that the serial pin is held high, then pulled low, this makes sense though from a communication point of view, if the connection is lost, the pin is not pulled high and it is easy to see that error pretty quickly. This also explains the AND gate.
Anyway, I was able to wire things up and hooked up an LED on the output side of the AND gate and could see the LED blink when a serial signal was being sent by the Arduino.
I have yet to put this in line between the RPi and Tic, that will be my next test.
