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Forum Index : Microcontroller and PC projects : LCD code
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VK6MRG Guru  Joined: 08/06/2011 Location: AustraliaPosts: 347 |
Looks like eBay is the best for a test unit to experiment with, less than $10 delivered.  Its easier to ask forgiveness than to seek permission! ............VK6MRG.............VK3MGR............ |
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| Ray B Senior Member  Joined: 16/02/2007 Location: AustraliaPosts: 219 |
Found / Tested source of low cost 20 x 4 backlit LCD. When ordered cost me AU$9.58 inc shipping - see price slightly increased today. 9 days from ordering from HongKong to Perth - received it today through Aussie Post Example of James Code Running on the display attached http://cgi.ebay.com/HD44780-20X4-Character-LCD-Display-BLUE- backlight-1-pcs-/380349890122?_trksid=p4340.m263& picture attached2011-07-13_223227_20x4_LCD_on_MM.pdf RayB from Perth WA |
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Keith @ Senior Member Joined: 19/06/2011 Location: AustraliaPosts: 167 |
Ray Thanks for the picture ... it really does paint a thousand words ... particularly the way you have done the pins for the ribbon cable and the printing of the pin outs. Good work on the LCD too. I'm keen to get get one working with the MM embedded version. Keith The more we know, the more we know we don't know ! |
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James_From_Canb Senior Member Joined: 19/06/2011 Location: AustraliaPosts: 265 |
I now have a 17 x 10 prototype board. I think it's supposed to be for Arduinos, but it does a good job of supporting a 16 pin LCD screen. It was an interesting Saturday afternoon project to fit it all in - and I still had one row left over! I did my MM to prototype board connection differently to Ray. I put the pins in order. The cable split is messier, but less confusing for me. Here's a photo of the whole system 
and one of the prototype board. 
I particularly like the 10K Resistor Network which has 6 x 10K resistors in one unit. It's the flat blue unit in front of all the yellow and brown cables. That made life a lot easier. I'm really starting to enjoy this. 10/10 for the Maximite! James My mind is aglow with whirling, transient nodes of thought careening through a cosmic vapor of invention. Hedley Lamarr, Blazing Saddles (1974) |
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| VK6MRG Guru Joined: 08/06/2011 Location: AustraliaPosts: 347 |
James, I got my LCD today.
Any chance of the schematic for your design? Its easier to ask forgiveness than to seek permission! ............VK6MRG.............VK3MGR............ |
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| James_From_Canb Senior Member Joined: 19/06/2011 Location: AustraliaPosts: 265 |
I don't have any schematic - I just followed Geoff's new LCD.pdf diagram. It's in the MMBasic Library V1.4 zip file available from Geoff's site. I'll PM you my LCD test harness program though. It's very much a work in progress, but it will allow you to change each command bit using a menu, so you can see the results on your LCD screen. James My mind is aglow with whirling, transient nodes of thought careening through a cosmic vapor of invention. Hedley Lamarr, Blazing Saddles (1974) |
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| James_From_Canb Senior Member Joined: 19/06/2011 Location: AustraliaPosts: 265 |
I've rewritten my original LCD program so it's more useful. I'd like some comments on what should be added or changed before I finish it up. Here's some brief notes about it. It follows Julyan Ilett's LCD tutorial Part 1 and Part 2 closely. If you're new to using LCD screens you should read them. You'll need to change lines 120 and 130 to include the number of lines and columns on your LCD screen. It's split into two menus - one sets control values, the other displays text. For your first try, I suggest you just start the program, select option 8, enter 1,1 then select option 12 and display a message. The message display section doesn't change any controls. It's up to you to clear the screen, select cursors, set the line and column where you want the message etc. I didn't want any of my code disturbing the control settings you select. Hence the name LCD_Explorer. You're exploring what the LCD control settings do. Lines and Columns start at 1, not 0. You can enter text into areas of memory that will never be displayed. Scrolling behaves differently on 2 and 4 line displays. Even though you may have a 4 line display, the control chip treats it as a 2 line with output split to different places. When you see scrolling, you'll see the consequences. Some chunks of code are not implemented yet, and some code could be enhanced - like the custom message code - it scrolls across a whole line. With a bit of tweaking it could just scroll over a subset of a line. Anyway, let me know how it could be improved. Once it's complete I'll submit it to Don's site along with proper documentation. Thanks James 2011-07-30_164429_LCD_Explorer.zip My mind is aglow with whirling, transient nodes of thought careening through a cosmic vapor of invention. Hedley Lamarr, Blazing Saddles (1974) |
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| Ray B Senior Member Joined: 16/02/2007 Location: AustraliaPosts: 219 |
james, excellent clear coding with lots of comments Regards from Bali. RayB from Perth WA |
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| James_From_Canb Senior Member Joined: 19/06/2011 Location: AustraliaPosts: 265 |
Well, I didn't get any comments about functionality. Either only one person looked at it, or it was almost perfect. Which it wasn't. The cursor direction only went one way, there were code stubs for missing functionality, and it was really clunky. Here's my next version. All the exercises in part 1 of the tutorials work, except it doesn't handle 8 bits, and it doesn't read values from the LCD (yet). Also, the "Write to CG RAM" is rudimentary, and is only there to show how it can be done. Try this version. I reorganised the menus to more strictly follow the split between control and display. The Control Menu now just sets control bits, and the Display menu lets you test the results. One useful change is that you can pre-select the display option. Instead of pressing D to get to the Display menu, then (for example) 3 to choose option 3, you only need to enter D3. If you want to code a module for it, write a separate .BAS file for it, starting from line 40,000, load LCD_Explorer, then merge in your code. It will run from the main menu. I had one weird bug. I set up constants at the start of the program renaming pins 13 to 16 to D4 to D7, and changed Geoff's "Write to LCD" routine to use those names, for instance pin(13) = xxx was changed to pin(D4) = xxx. Rubbish was written to the LCD screen and my case power LED light went out. I tried adding pauses in case it was a timing issue, but it didn't help. I went back to just using the numbers. Anyway - have fun with the program and let me know if you find any problems or if you have any suggestions on how to improve it. I've included the change log in case you want to see the fixes and improvements so far. 2011-08-05_230823_LCD_Explorer_1-1.zip 2011-08-05_231158_LCD_Explorer_Change_Log.zip James My mind is aglow with whirling, transient nodes of thought careening through a cosmic vapor of invention. Hedley Lamarr, Blazing Saddles (1974) |
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Geoffg Guru Joined: 06/06/2011 Location: AustraliaPosts: 3194 |
The power light going out is not a good sign... it could mean that the MIPS CPU had thrown an exception and crashed. Do you have a code fragment that demonstrates this effect? Geoff Geoff Graham - http://geoffg.net |
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| James_From_Canb Senior Member Joined: 19/06/2011 Location: AustraliaPosts: 265 |
Well, the program kept working, so if it crashed it recovered well. Another possibility is that pin(PinName) did not resolve the value PinName so it was interpreted as zero, which would alter the status of pin(0), the power LED controller. The only problem with that theory is that other code did not turn it back on, so it was not consistent. I'll see if I can replicate the problem with your original LCD code, otherwise I'll modify mine to the minimum needed to demonstrate it. Your laptop obviously survived the corrugations on the Gibb River Road. Welcome back to civilisation. My mind is aglow with whirling, transient nodes of thought careening through a cosmic vapor of invention. Hedley Lamarr, Blazing Saddles (1974) |
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| James_From_Canb Senior Member Joined: 19/06/2011 Location: AustraliaPosts: 265 |
I couldn't get your original LCD code to fail by changing the pin numbers to constants. Here's some code where the display on the LCD is different depending on whether you use constants or numbers to select the data pins (it's fine with Enable and RS). My power LED turns off if I use constants. James 210 _C_L1_Start = 0 220 _C_L2_Start = 64 230 _C_L3_Start = 20 240 _C_L4_Start = 84 250 ' 260 DIM _Offset(4) 270 _Offset(1) = _C_L1_Start ' load all the offsets into an array 280 _Offset(2) = _C_L2_Start 290 _Offset(3) = _C_L3_Start 300 _Offset(4) = _C_L4_Start 310 ' 320 DIM _Text$(4) ' An array to hold the 4 display lines 380 ' 390 _Text$(1) = "Hello World, I'm " ' load initial display values for the screen 400 _Text$(2) = "a Maximite LCD " 410 _Text$(3) = "communicating with a" ' if you have a 2 line display, there's no harm leaving these extra lines here 420 _Text$(4) = "4 line HD44780 LCD. " 430 ' 440 ' Define the pin names 450 RS = 11 460 Enable = 12 470 D4 = 13 480 D5 = 14 480 D6 = 15 490 D7 = 16 500 ' 510 ' define LCD screen values 560 _LCD_Lines = 4 570 _LCD_LineLength = 20 580 ' 10020 Input "Run display using Constants or Numbers (C,N) "; RunType$ : RunType$ = UCASE$(RunType$) 10030 GOSUB 29000 'Initialise the LCD 10070 GOSUB 20000 'Show that text displays differently under the 2 options 10090 END 10100 ' ------------------------------------------------------------ ------ 10110 ' 20000 ' 1. Display the default messages for the lines (defined at beginning of the code) 20010 ' ----------- ------------------------------------------------------------ ------ 20020 ' This ignores whatever DDRAM location you have set up with the Control menu. 20030 ' It relies on the values for _C_Lines and _C_LineLength being correct. 20040 ' 20050 for _Line_out = 1 to _LCD_Lines 20060 _LCD_byte = 128 + _Offset(_Line_out) : GOSUB 30000 ' select the output line on the LCD 20070 for _LCD = 1 to _LCD_LineLength 20080 _LCD_byte = ASC(MID$(_Text$(_Line_out), _LCD, 1)) 20090 pin(RS) = 1 : GOSUB 30000 ' send the character 20100 next _LCD 20110 next _Line_out 20120 ' 20130 RETURN 29000 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' '''' 29010 ' Initialise the LCD 29020 ' 29030 FOR i = 11 TO 16 : SETPIN i, 9 : NEXT i ' set the pins to Open collector digital output to 5V 29040 _LCD_byte = &B0011 : GOSUB 30100 ' reset 29050 _LCD_byte = &B0011 : GOSUB 30100 ' reset 29060 _LCD_byte = &B0011 : GOSUB 30100 ' reset 29070 _LCD_byte = &B0010 : GOSUB 30100 ' 4 bit mode 29080 _LCD_byte = &B00101100 : GOSUB 30000 ' 4 bit, 2 lines (or 4 lines) 29090 _LCD_byte = &B00001100 : GOSUB 30000 ' display on, no cursor 29100 _LCD_byte = &B00000110 : GOSUB 30000 ' increment on write 29110 _LCD_byte = &B00000001 : GOSUB 30000 ' clear display 29120 pause 2 29130 RETURN 30000 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' '''' 30010 ' Send a byte to the LCD 30020 ' the data to be sent is in _LCD_byte 30025 ' USE CONSTANTS TO CONTROL PINS 30030 IF RunType$ = "N" THEN GOTO 40000 30040 Pin(D4) = _LCD_byte AND &B00010000 ' output the 1st 4 bits 30050 Pin(D5) = _LCD_byte AND &B00100000 30060 Pin(D6) = _LCD_byte AND &B01000000 30070 Pin(D7) = _LCD_byte AND &B10000000 30080 pin(Enable) = 1 : pin(Enable) = 0 ' tell lcd to accept data 30100 ' Entry point to send just 4 bits to the LCD 30105 IF RunType$ = "N" THEN GOTO 40100 30110 Pin(D4) = _LCD_byte AND &B00000001 ' output the 2nd 4 bits 30120 Pin(D5) = _LCD_byte AND &B00000010 30130 Pin(D6) = _LCD_byte AND &B00000100 30140 Pin(D7) = _LCD_byte AND &B00001000 30150 pin(Enable) = 1 : pin(Enable) = 0 : pin(RS) = 0 ' tell lcd to accept data 30160 RETURN 30170 ' 40000 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' '''' 40010 ' Send a byte to the LCD 40020 ' the data to be sent is in _LCD_byte 40030 ' USE NUMERIC VALUES TO CONTROL PINS 40040 Pin(13) = _LCD_byte AND &B00010000 ' output the 1st 4 bits 40050 Pin(14) = _LCD_byte AND &B00100000 40060 Pin(15) = _LCD_byte AND &B01000000 40070 Pin(16) = _LCD_byte AND &B10000000 40080 pin(Enable) = 1 : pin(Enable) = 0 ' tell lcd to accept data 40100 ' Entry point to send just 4 bits to the LCD 40110 Pin(13) = _LCD_byte AND &B00000001 ' output the 2nd 4 bits 40120 Pin(14) = _LCD_byte AND &B00000010 40130 Pin(15) = _LCD_byte AND &B00000100 40140 Pin(16) = _LCD_byte AND &B00001000 40150 pin(Enable) = 1 : pin(Enable) = 0 : pin(RS) = 0 ' tell lcd to accept data 40160 RETURN My mind is aglow with whirling, transient nodes of thought careening through a cosmic vapor of invention. Hedley Lamarr, Blazing Saddles (1974) |
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| Geoffg Guru Joined: 06/06/2011 Location: AustraliaPosts: 3194 |
OK, thanks. Thankfully it is not an exception so there must be a subtle bug in the handling of the I/O pins. I cannot see what it could be and without an LCD I cannot reproduce it so I will keep looking through the source trying to find it. Yes, the laptop made it but I almost did not. I contracted a tropical infection in my leg and ended up spending 4 days in Derby hospital. I am now recuperating in a luxury hotel in Broome which sort of makes up for the ordeal. Geoff Geoff Graham - http://geoffg.net |
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| James_From_Canb Senior Member Joined: 19/06/2011 Location: AustraliaPosts: 265 |
I wouldn't put any effort into it, especially as you don't have the gear to track it down. It's a low priority bug with an easy workaround. The main thing is that people know about it and use numbers until the problem is corrected in a later version. James My mind is aglow with whirling, transient nodes of thought careening through a cosmic vapor of invention. Hedley Lamarr, Blazing Saddles (1974) |
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| James_From_Canb Senior Member Joined: 19/06/2011 Location: AustraliaPosts: 265 |
AAARGH. A thousand pardons. Two thousand. I could have sworn I checked my line numbers. There were two line 480s, so D5 was never defined. I wish I could put that in even smaller print. I'm an idiot and have no idea how that got past me.  I really apologise for raising it. Next time I'll be much more careful.
Time to find an editor that highlights duplicate lines. My mind is aglow with whirling, transient nodes of thought careening through a cosmic vapor of invention. Hedley Lamarr, Blazing Saddles (1974) |
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bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2914 |
Ahahaaa, Good Work James, I looked at your code and couldnt see much wrong and my adaptation of Geoff's LCD routine (I modified to use the Arduino LCD+switch shield on Don's DonDuino Cross PCB) worked fine using variables so I couldnt see what was wrong but with TWO line 480 would negate the first line 480... Much better if we can do away with line numbers all together and use labels... but all for a later firmware. Mik Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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