After getting the Jump Bug straightened out, I decided to double-check the 65c22s and make sure they worked as expected and then try to get the LCD display working. I tested all four 65c22s by hooking both ports up to an LED bar and then sending a bit pattern to each one. After they all passed that test, I forced an input bit pattern by tying the port pins to alternating ground and +5V. Everything worked as it should. That means all the data lines, address lines and chip selects were wired correctly. I put the LCD back on the bus and gave it a shot… no go.
After double-checking all the wiring, then triple-checking, then quadruple checking, I went back to the datasheet. There is something in there about an auto-initialization of the HD44780 U controller. The chip has to go from 0.2V to 4.5V in between 0.1 and 10 milliseconds. I put the power lines to the chip on the oscilloscope and discovered it was taking 30ms or so for the voltage to reach 4.5. I’ve tried a couple of experiments to see if I could get it to work, but still haven’t had any success.
I decided to move on to the SC28L92 dual UART. I had some issues with it too. I found some sample code in the datasheet for a similar chip and tried that. I got input from a terminal on another computer to work, but I still couldn’t get output from ROL to the remote terminal to show up.
I started by checking all the lines with a multimeter and the oscilloscope and determined nothing was even coming out of the chip. I looked over the bit of code I used from the datasheet and found the last instruction was enabling RX but not TX! I set the appropriate flags in the register value to enable TX and tried again. The result is in the photo.
So now, I not only have a way for ROL to communicate to the outside world, but I also have a way for the outside world to communicate with ROL!
At this point, the LCD module is way on the back burner. I’d rather use the serial port for output anyway. Though, I still think I’m on the right track with the initialization procedure and too slow voltage rise time.