I have an LPC17 core built, boot loader installed, MIDIBox NG uploaded, and SD card connected. I’m still waiting on some DIN/DOUT boards, so for now I only have a 2x40 LCD to test with.
And that’s where I’m stuck… LCD powers on, MIOS studio appears to detect it (I don’t get a “no response” msg), I’ve checked the brightness and contrast pots, but all I see are bars/boxes/rectangles on the top line. So in no particular order, here’s what I’ve looked at so far:
Continuity check between shift register outputs and J15A/B pins is OK
Enabled display on 2nd LCD using mios32 boot loader update application and tried connecting the lcd to J15B - No change
Replaced 74HC595 IC with a new part - No change
So now I’ve moved on to testing with the console using “testlcdpin”, but I’m having trouble interpreting the results. With the LCD disconnected, and testing all pins on J15A with a meter, here are my findings:
ON J15A/B pins RS, RW, E1, E2 all measure from 0-3.3V as expected when changed from 0 to 1 at the console
Yesterday, d0-d7 stayed at 0V no matter what command I entered, but the console reported the expected logic-0 level at the d7 input pin
However, today I have just retested, and now get the message, “ERROR: D7 input pin shows unexpected logic-1 level!” “Please check the D7 feedback line on your core module!”
So… very confused now - any insight as to what I’m doing wrong or what I can try next? Thanks in advance!
So this is weird… while waiting for some advice, I made up a 1x DOUT board to test controlling outputs. It didn’t work at first, and traced the issue back to the shift register. I thought I’d try that using that same 595 in the core module since I knew it was good, and what do you know, the LCD fired right up! But what’s strange is that the 595 that I previously used in the core module, worked fine in the DOUT board. Maybe it wasn’t seated quite right in the socket?
Thanks TK - Confirmed that all the SR’s I have are 74HC595, LCD I’m using is 5V. I’m in Taiwan, wonder if I got some flaky components? (Although they are labelled as TI parts)
Good point, but I’m afraid to touch it since I got it working! I’d like to work on some software for a while before go back to troubleshooting hardware…
I have the same problem, except it’s a new STM32F4 core, and all the results from testlcdpin are correct, both by its self-test and by my scope measurement. Tried replacing the shift register with one known good, no change. Backlight and Contrast pots perform correctly. On startup the bootloader test app says “Initializing LCD #1” with no “error” message on the next line, so it seems the core can talk to the LCD just fine. But still the bar on the top line. Anyone have any ideas? Is there something in the bootloader configuration I could be missing? This kind of problem even makes us “experienced” folk feel like n00bs sometimes…
One thing to mention is that I’ve always used 10k resistor packs for R33, the LCD line pullups, instead of the listed 1k, because I would have to order extras of those specifically. This has worked fine for two LPC17 cores, with no LCD problems at all. But could it be that with the STM32F4’s lower voltage of 2.95V, that’s not quite enough current now? I’ll take it apart and solder on some 1.5k resistors in parallel if need be, but I’d rather not have to do that.
One thing to mention is that I’ve always used 10k resistor packs for R33, the LCD line pullups, instead of the listed 1k
This is the problem.
Some time ago somebody else reported the same problem in this forum with the STM32F4 board (can’t find the thread) and it turned out that this was because he used 10k pull-up resistors.
Thanks, it works great now.