Since I'm constantly working on some wacky interfacing project or other, I figured I'll start a thread on the subject since I have a question.
I have been working on connecting the TI's parallel port to a Raspberry Pi equipped with the Pi camera to capture a picture on the TI. Since the Rpi is a 3.3V system, I have had to figure out how to achieve bidirectional logic level shifting between 3.3 and 5 volts. I found this 74LVC245 8-bit logic level shifter on Adafruit and I created a primitive communication protocol between the TI and the Rpi to control it. It worked quite well, and I am able to send data and control signals bidirectionally, but the thorny problem I am currently encountering is spurious signals generated somewhere triggering unwanted events and messing up the synchronization of the data transfers.
Each byte of the image captured by the Rpi is transmitted to the TI upon receipt of a HANDSHAKEOUT high signal from it to port 23 on the Rpi, and the cycle subsequently repeats until all the bytes are sent. What is happening is that there are spurious HSKOUT high signals somehow being generated, wreaking havock with the process. As a test, I set up the TI side to hold HSKOUT low after receiving the first byte, and yet the Rpi kept trying to send new bytes in for a few cycles before stopping and waiting. It's almost reminiscent of key bounce, except that there are no physical keys or switches involved here.
I have connected all the unused inputs of the 245 to ground or Vcc without any noticeable improvement, and I am currently at a loss as to how to eliminate that problem.
If anyone here has any suggestions, I would be very grateful to hear them. I am running out of hair to pull!