LCD replacement, ST7565 vs ST7567, Vm and Vg - Page 1
Forum section: electronics / projects

author: KhronX
author_rank: Frequent Contributor
timestamp: July 02, 2023, 09:52:48 pm
content: It's been a while since i've been active around these parts, but better late than never..?But more to the point - i recently finally "graduated to the big boys' league", and grabbed a silly good deal on an older 2-channel JBC soldering station, with a whole bunch of extras. Unfortunately though, somehow the LCD managed to get smashed in, along with the outside protective window, seemingly in transit. At least the seller sent me back a 10% refund, so i'm not resenting that.Fortunately, the week before i noticed the aforementioned one, i had taken delivery of a used "compact station", also from JBC. Just to make sure everything else works, i took the liberty to temporarily transplant the LCD from the latter to the former.Now to the less fortunate parts...All the help i got from JBC themselves was getting me in touch with their local distributor, to get an offer of a refurbished newer 2-channel unit, for about as much as i had paid for the one i got, with all the extras. Thanks, but no thanks.Both stock LCD's seem to be made by Powertip, and the model is PE12864WRM-001HC1Q, as per the markings on the rear. "Of course", it's long discontinued. No real complete datasheet to be found online, save for some drawings and pinouts.https://www.digchip.com/datasheets/parts/datasheet/371/PE12864-001-C1-pdf.phphttps://www.datasheet.live/pdfviewer?url=https%3A%2F%2Fpdf.datasheet.live%2F6fa6b64e%2Fpowertip.com.tw%2FPE12864-001.pdfOn the bright side, TME seems to carry at least some Powertip LCD's, and as luck would have it, even one in the exact size and format of the busted one.https://www.tme.eu/Document/a7c96086bff062472a0ca6eb3c1d2f21/PE12864WRF-055-H-Q.pdfBUT... It uses the newerST7567controller, as opposed to theST7565of the stock one.Most of the pinouts seem common, but the '65 needs a lot more external capacitors for all the charge pumps for bias voltages etc.I ended up carefully removing the FPC connector from the JBC board, applied some Kapton tape over the pads that would need to connect elsewhere, and soldered the connector back. Despite the newer LCD's datasheet claiming that all the "NC" pins should be left floating, the copper pads on its flex-connector are not connected to anything. I reused the connections one of the existing on-board capacitors though, for the V0-XV0 connection.From what i could understand, Vg is generated internally inside the controller, and only needs a capacitor to ground. I have zero clue about the Vm connection though. In the chip datasheet, it seems to not get connected to the outside world, only to some test pad. Only other relevant mentions of Vm is that it's supposed to be 1/9 * V0-XV0, while Vg should be 2/9 * V0-XV0.As it stands, with a 1uF cap between V0 and XV0 pins, and another 1uF between Vg and ground, the replacement LCD isblank. And i'm quickly running out of ideas...Does the Vm also need a capacitor to ground? Any LCD gurus in the house?

author: jpanhalt
author_rank: Super Contributor
timestamp: July 02, 2023, 10:18:34 pm
content: I use the ST7567 in a current project. My connections are exactly as in the datasheet. (https://www.crystalfontz.com/controllers/Sitronix/ST7567/)I assume you are using a serial interface. I use SPI. I found it quite sensitive to EV. Here is the code for that section in PIC assembly. While the code may not work for you, the settings may help. Do you have access to the code?Code:movlw 0xF8 ;set boost = x5, double command |B2call PutCMD+4 ; " |B2movlw 0x01 ; " |B2call PutCMD+4 ; " |B2movlw b'00100111' ;0x27, set Regulation Ratio = 6.5 |B2call PutCMD+4 ; |B2movlw 0x81 ;double command: Set EV |B2call PutCMD+4 ; " |B2movlw 0x2C ;EV = 44 dec |B2call PutCMD+4 ; " |B2movlw b'00101111' ;0x2F,set voltage follower on |B2After I got over that hurdle, I like the display. It is very quick, and the only drawback I faced was the inability to read it using a serial interface. It is so fast, that reading ready was not an issue.John

author: KhronX
author_rank: Frequent Contributor
timestamp: July 02, 2023, 10:32:24 pm
content: Thanks for chiming in.But, if you've read everything in the original post, this is about retrofitting a newer LCD into a JBC soldering station. The pinout and connections of the configuration pins indicate that it's used in 8080 parallel mode.I'll be honest, i haven't compared the initialization routines between the '65 and '67 datasheets - on one hand, because that's "above my pay grade" (coding was never my thing), and on the other hand, because i don't have access to the source code of the dsPIC used here.

author: jpanhalt
author_rank: Super Contributor
timestamp: July 02, 2023, 10:46:32 pm
content: Quote from: KhronX on July 02, 2023, 10:32:24 pmThanks for the additional information. That still doesn't change my comment about those settings. I spent a considerable amount of time getting the contrast to work and have no idea whether the ST7565 would work with the same settings. Do you?