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Old 01-20-2008, 04:48 AM   #1
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Unhappy linux driver needed for 20x4 LCD connected via parallel to USB cable

hi guys! oh please help us (me and groupmates) with this..
we have here a 20x4 character LCD to be connected to a parallel port. we borrowed a miniPC for a project, and that miniPC (running on puppy linux doesn't have a built-in parallel port, only a VGA port, LAN port and 4 USB ports. so we bought a parallel to usb cable/adapter. the problem now is we can't find the right driver to make the LCD work. we tried lcdmod (error was: "LCD: no parport found at 0x378")and lcd4linux, but none of them worked. we are really on a rush. we'll appreciate your immediate response. thanks!!!

by the way.. we're not sure if our LCD is somewhat similar to Hitachi standards, but here's what we have -->

Last edited by cayo; 01-20-2008 at 05:04 AM.
Old 01-21-2008, 05:05 PM   #2
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I found some info on the SPLC780D driver chip and at first glance looks similar to the Hitachi standard. Do you have a manual for the display? Looks like the apps are looking for real hardware port i.e. 0x378.

I've never played with a USB parallel port adapter but trying to control hardware might be difficult. I do have a mini-itx system with a USB LCD display but have not had time to figure it out yet.

libusb might be a good starting point for figuring out how to access the device.

Last edited by michaelk; 01-21-2008 at 09:51 PM.
Old 01-22-2008, 09:27 AM   #3
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our LCD doesn't have any manual. we tried to change the base address on the code of lcdmod (from 0x378 to "/dev/usb/lp0", since the parallel to usb cable was detected as usblp), the error now is "LCD: no parport found at 0xc8136aff". we tried another driver (usblcd-0.1) and there, you have to put the vendor and product ID on the code. we typed the IDs of the parallel-usb adapter and it was detected. but then, it still didn't work. the value of usb_control_msg(with some parameters here..) is -1, which supposed to be >0. we think that the miniPC can only detect the parallel-usb adapter because it has the direct connectivity with the miniPC, leaving the LCD connected through that adapter undetected.


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