Post by thread:4X16 LCD (again)

Hi all, I am trying to get an Optrex 4X16 LCD to work (HD44780) using the code from Peter Ouwehand's home page. The catch is I am using a 16C74A as opposed to the 16C84. Has anyone else tried this? I turn the circuit on and the first and third lines of the LCD are filled in with block characters, the second and fourth lines are blank. I am using the full 8-bit interfacing. FRUSTRATION!!!!!! Help me!! Help me!!!! I cannnnnn't seeeee!!!!! Thanx in advance Jay Mielke

Jay Mielke wrote: > I am trying to get an Optrex 4X16 LCD to work (HD44780) using the code > from Peter Ouwehand's home page. Ah yes. I didn't have that filed under his name, but it is one of my *major* references! > The catch is I am using a 16C74A as opposed to the 16C84. Has anyone > else tried this? Should work fine. Minimal differences. > I turn the circuit on and the first and third lines of the LCD are > filled in with block characters, the second and fourth lines are > blank. I am using the full 8-bit interfacing. The display uses "two-line" mode. The "second" line is as you have found, actually the second and fourth lines. Looking for "Function Set" in http://www.iaehv.nl/users/pouweha/lcd0.htm#instruction_set you will note that you have to set up bit 3 ("N") as a "1". For you, the command value will be $38 or $3B. He appears to have fixed the typo I reported. Good ;-) Note the display addresses of the four lines. They are tabulated in http://www.iaehv.nl/users/pouweha/lcd.htm which *also* reminds you of the correct value for "N". The first line scrolls automatically to the third, and the second to the fourth. -- Cheers, Paul B.

Jay Mielke wrote: > I am trying to get an Optrex 4X16 LCD to work (HD44780) using the code > from Peter Ouwehand's home page. Something worries me however. Marc Simons' example of interfacing ( http://www.iaehv.nl/users/pouweha/lcd_examp.htm ), though it *will work*, is IM(NS)HO rather kludgy. R1, C5, T1 and R2 make the code time-critical and are entirely unnecessary. RS should instead be commoned either *directly* to the Clk pin 3, or to D (Data) on the 4092. The code must be adjusted to suit, but is actually simpler and ... faster! Now, you do need to delay to permit the HD44780 to do its job, but in general if you use concise code to load the commands/ data, you can then perform other tasks whilst waiting. Also, pin 1 of the 4092 (Strobe) might as well be tied high instead of to the EN. The circuit certainly works as posted because the HD44780 latches the data on the trailing edge of EN, so the latch function is entirely superfluous. -- Cheers, Paul B.

I haven't read the code but if it was meant for the '84 and uses 8 bit data bus, PORTA was probably used for control lines. Remember on '74 that PORTA has analogue to digital converters which defualt to analogue mode on power up. You have to set them digital mode. That's what I would check. On Fri, 14 May 1999, Jay Mielke wrote: {Quote hidden}> Hi all, > I am trying to get an Optrex 4X16 LCD to work (HD44780) using the code from > Peter Ouwehand's home page. The catch is I am using a 16C74A as opposed to > the 16C84. Has anyone else tried this? I turn the circuit on and the first > and third lines of the LCD are filled in with block characters, the second > and fourth lines are blank. I am using the full 8-bit interfacing. > FRUSTRATION!!!!!! Help me!! Help me!!!! I cannnnnn't seeeee!!!!! > > Thanx in advance > Jay Mielke >

What i did to debug my LCD troubles was make a delay routine of about a second or two, then call it each time the enable line changes state, so i could use a logic probe to diagnose things. ------------------------------------------------------------------------------ A member of the PI-100 Club: 3.1415926535897932384626433832795028841971693993751 058209749445923078164062862089986280348253421170679 On Fri, 14 May 1999, Jay Mielke wrote: {Quote hidden}> Hi all, > I am trying to get an Optrex 4X16 LCD to work (HD44780) using the code from > Peter Ouwehand's home page. The catch is I am using a 16C74A as opposed to > the 16C84. Has anyone else tried this? I turn the circuit on and the first > and third lines of the LCD are filled in with block characters, the second > and fourth lines are blank. I am using the full 8-bit interfacing. > FRUSTRATION!!!!!! Help me!! Help me!!!! I cannnnnn't seeeee!!!!! > > Thanx in advance > Jay Mielke >

When you apply power to pins 1 + 2, polarization voltage to pin 3 on a 4xN LCD, the first and third lines comes up in black characters since it is "power up preset" to one line mode, so the first line is on (remember that the first line is broke in two and it extends as the "third" line). If your PIC can't change that, it means that your device is unable to reprogram the unit to 2 lines. If you don't have an osciloscope to debug it, just insert delays of 1 minute or more between data sent to the LCD, so you could measure the state of the lines using a simple voltmeter. Just measure all the 14 lines after each change, make a map and compare to what it should be. Wagner Lipnharski

Where ya been, Wagner ? On Sunday, May 16, 1999 9:49 AM, Wagner Lipnharski [SMTP:spam_OUTwagnerlTakeThisOuTEARTHLINK.NET] wrote: {Quote hidden}> When you apply power to pins 1 + 2, polarization voltage to pin 3 on a > 4xN LCD, the first and third lines comes up in black characters since it > is "power up preset" to one line mode, so the first line is on (remember > that the first line is broke in two and it extends as the "third" > line). If your PIC can't change that, it means that your device is > unable to reprogram the unit to 2 lines. If you don't have an > osciloscope to debug it, just insert delays of 1 minute or more between > data sent to the LCD, so you could measure the state of the lines using > a simple voltmeter. Just measure all the 14 lines after each change, > make a map and compare to what it should be. > > Wagner Lipnharski

I have a project which also uses the 16c74a. Sometimes I have the same problem with lines 1 and 3; however, it is caused because I forget to turn off my debug switch. This switch comments out a power up delay for the LCD. ( I do this for simulation) So my first comment is confirm that your power up delay is long enough. I also experienced the problem when I replaced one brand of LCD with another. I had to insert a small delay in my busy flag routine. (I monitor the busy flag pin14 for completion of the command) I do not know for sure why I had to do this, but it works now. Good Luck Kevin