(Graphic LCDs) Negative voltage generator?


New member
Hey there,

I'm considering buying a graphic LCD from this site, however I am not sure as to the purpose of a negative voltage generator.
(The CFAG12864B-WGH-V has one where the CFAG12864B-WGH-N does not).
It only costs a couple of dollars... without one built-in do I build my own?
Also, the CFAG12864B-WGH-N datasheet (CFAG12864BWGHN.pdf) confused me. After finally discovering that the CS1, CS2 lines were not "chip select" but "column select" lines, I wondered why they would be connected directly to the CPU, as shown on page 8 of the PDF. Should I be using these lines as part of the address bus or data bus or PIO or...? What has been used before?
I'm using a Z80 (at 20Mhz). In fact this raises a different issue, the timing. At this frequency, the R/W line is enabled for only 150ns, whereas the LCD needs around 450ns. As far as I can tell this is possible with the Z80 using wait states (i.e. holding the WAIT pin on the Z80 active for the required 450ns after every IO request using the LCD). Well, I'm also really looking for confirmation that this sounds correct-ish.

I've also just noticed on the same page.. "EL B/L should drive directly from A/K". The backlight? This confuses me more since the previous page states how A and K are Not Connected.

The table on page 10 is fine, and shows the D/I and R/W lines correctly -- but the following guide to the different instructions does not (apparently everything is an instruction write).

To be honest I'm a little dissappointed there is no simple example for things such as writing to the display. The data's all there -- but there are mistakes in even that!
I apologise for my nastiness, but I'm just not the sort of person who likes to spend money and only then find out it doesn't work as described/expected.

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