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Messages - richardwright

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Great, thank you.  I did see the diagram in the data sheet, in addition to the internal wiring diagram in the ST7066U manual showing pull-ups on RS and R/W but not E - both great references.  It seemed clear but I wanted to get a confirmation just in case.

We are stuck on the use of the NHD-0420H1Z-FL-GBW-33V3.  The display does illuminate when powered and initialized but no cursor or characters are ever visible.  It also seems as if the DDRAM addresses are not incrementing when data is written to them or event when an explicit address command is sent to the controller.  Oddly, the BF does seem to be working...

I was hoping there was a requirement for external components and that perhaps floating lines were responsible - on the off chance they would stop the controller from initializing properly if they were absent.


Given that is not the case - can you suggest a means to troubleshoot the internal state of the controller?  How can we verify it is in fact initialized?  Is there, for example, a DDRAM location I can attempt to read that holds the current Function Set data?  I could write various values via Function Set and read them back to verify their application.

Another thought is that perhaps the voltages to VDD, V0, and LED+ are misconfigured - high V0 for example (V0 = VDD).  But if that were the case I would expect the call to set the AC or calls to write characters would result in those address values coming back with the BF.

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Can anyone confirm the NHD-0420H1Z-FL-GBW-33V3 does or does not require pull-ups on E,RS,andR/W?  Additionally, in 4-bit mode are there internal pull-downs on the low nibble lines.  Is the external circuit expected to provide either pull-ups or pull-downs in 4-bit mode on any lines?

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Character LCDs / Re: Issue with reading busy flag in 4 bit mode.
« on: December 09, 2014, 08:50:54 AM »
Just to clarify here.  In the manual for the ST7066U controller on page 26 there is a series of routines exemplifying 4-bit operation.  One of the routines is a check busy path.  It seems in that example the busy flag appears to be transferred in the first nibble.  The pins are read as part of the first strobe when E is set high but the pins are ignored when E is strobed the second time.


Does the byte order varying between LCD models with similar controllers?


>>Snip
CHK_BUSY: ;Check Busy Flag
PUSH A
MOV P1,#FFH
$1
CLR RS
SETB RW
SETB E
MOV A,P1                <====This appears to be the only time the pins are read.  E is strobed both here as well as a few instructions down though.
CLR E
MOV P1,#FFH
CLR RS
SETB RW
SETB E
NOP                       <====The pins are ignored
CLR E
JB A.7,$1
POP A
RET

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