Debugging the LCD Display Driver and Hardware

This week i worked on the 640x480 pixel b&w LCD terminal.  Soldering was easy, but fixing all the bugs took some time. I also had  to do some changes to the terminal code because i realized that i was using the LCD upside down.

I connected the LCD and powered the board through the programming  header. Off course nothing worked, except for the display refresh routine, which brought up a picture of the erased DRAM cells. Step by  step i brought up more functions: Erase screen, print characters, read  and write whole pixel lines and scrolling. I had to add some nops to the DRAM read and write timing, because the data goes through series resistors which create some delay. For the next board i'll reduce them slightly. Then printing of standard-size characters with 4 attributes in all combinations works.

 Finally one last important step: Attach it via serial line to USB to my Mac. Nothing worked. I adjusted the Baudrate on both sides. I printed text from the LCD terminal on the serial line in an endless loop. There was no signal on the TxD line. Why? But there seemed to be a signal on the RxD handshake line. ... ???

I had connected data lines to handshake and handshake to data lines on the board. :-(. Fixed it with a cutter, solder and wire. Tested. Worked. :-)

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