AVR-Chat

Tim et al,

Thanks all for lots of useful advice. I've tried various recommendations 
but haven't fixed the problem. I added a loop counter to the busy flag 
check to limit the busy checking to max 1.6ms, then just went ahead and 
sent the instruction regardless of the busy flag. This didn't work.

I'm coming to the conclusion described by Tim below - it's probably an 
LCD quality problem and nothing I do with code, caps etc is going to fix 
it. I don't have the option to control power to the LCD but it's an 
option to consider for future designs.

Thanks again,
Mark


Tim Gilbert wrote:
> Mark,
> Being HD44780 compatible only means that they cloned the command set developed by Hitachi some 20 years ago.  In my collection of LCDs (and I have a lot of them), I've only ever seen 1 unit that had real hitachi HD44780 chips  (it's really old and required the 8 bit interface!).  The original LCD modules required several driver and controller chips to run the display.  That's way we now have displays, like the 16x4, where the pcb is twice as big as the glass.  Everything has changed except the archaic command set and the oversized footprint.
>
> I've run into this lockup problem once several years ago while trying to control a 1 HP motor.  Every so often the noise from the motor would lock up the LCD module.  The problem was related to the ribbon cable running to the display.  (That's why in all our prototype development kits we keep the lcd connection as short as possible.)  Another option is to control the power to the LCD module so you and reset it if it locks up.
>
> There is a huge difference in the quality of LCD modules and I don't think the problem is with your design.  I wouldn't try to patch it if it's worked for 15 years; tell your purchasing agent to go back to the old supplier; he didn't save you any money.
>
> Regards,
>
> Tim Gilbert
> JEM Innovation Inc.
> 303-926-9053 (office)
> 303-437-4342 (cell)
> 720-890-8582 (fax)
> www.jeminnovation.com
> www.pdksolutions.com
>
>
>   ----- Original Message ----- 
>   From: Mark Nowell 
>   To: AVR-Chat@yahoogroups.com 
>   Sent: Wednesday, August 22, 2007 6:59 AM
>   Subject: [AVR-Chat] OT: HD44780 LCD lock-up - busy flag stays set
>
>
>   Apologies in advance for the thoroughly non-AVR question but I'm really 
>   tearing my hair out with an LCD problem and I'm sure there are some 
>   really clever/experienced LCD'ers here (grovel, scrape) ...
>
>   We've recently switched to yet another cheaper, brighter, 16x2, HD44780 
>   compatible LCD (Ampire AC162DY1LY). A small number of these latest 
>   displays lock-up after correctly initialising and executing a (variable) 
>   number of display commands. By "lock-up" I mean that the busy-flag stays 
>   set for at least 150ms, after which time the watchdog resets the micro, 
>   which then attempts to re-initialise the display, and fails, presumably 
>   because it's still busy. Display shows the last written text overwritten 
>   by blocks on the top line, bottom line blank. The display controller 
>   appears to still be alive because the successive E-cycles show different 
>   data-bit patterns for the alternate BF and AC3 cycles (4-bit mode).
>
>   The LCD driver code has been untouched over 15 years, several thousand 
>   displays and half-a-dozen different display types. I've double-checked 
>   the timings and they're not even close to marginal. Code below [ok, it's 
>   an 80C196 but the comments are in english - 12MHz - port writes take 
>   833ns, branches 833/1500ns - I'll claim it's a deliberate reminder of 
>   how what a marvel AVR RISC is].
>
>   Has anyone experienced anything like this? Should I suspect faulty 
>   displays? Or my code?
>
>   TIA,
>   Mark
>
>   void LMFWriteData( void ) {
>   /* on entry LMDATA contains DB0-7 */
>   /* check busy status */
>   asm bbc lmNoDisplay,0,checkBusyFlag ;
>   asm br lmfwdEnd ;
>   checkBusyFlag:
>   ioport1 = 0x2f ; /* rw=1, db4-7=weak1, e=rs=0 */
>   ioport1 = 0x6f ; /* e=1, db7->busy flag */
>   asm bbc ioport1,3,busyFlagClr ;
>   ioport1 = 0x2f ; /* e=0 */
>   ioport1 = 0x6f ; /* e=1, db7->AC3 */
>   asm br checkBusyFlag ;
>   busyFlagClr:
>   ioport1 = 0x2f ; /* e=0 */
>   ioport1 = 0x6f ; /* e=1, db7->AC3 */
>   ioport1 = 0x2f ; /* e=0 */
>   /* write instr */
>   asm ldb LMDATAHI,LMDATA ;
>   asm shrb LMDATAHI,#4 ; /* LMDATAHI.0-3=hi data */
>   asm andb LMDATA,#0x0f ; /* Clr LMDATA.4-7 */
>   asm ldb ioport1,#0x1f ; /* put rs=1,r/w=0,db4-7=weak1,e=0 */
>   asm addb ioport1,LMDATAHI,#0x50 ; /* e=1,db4-7=hi data */
>   asm addb ioport1,LMDATAHI,#0x10 ; /* e=0 */
>   asm addb ioport1,LMDATA,#0x50 ; /* put lo data,e=1 */
>   asm addb ioport1,LMDATA,#0x10 ; /* e=0 */
>   lmfwdEnd: ;
>   }
>
>
>
>    
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> [Non-text portions of this message have been removed]
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