Some Questions About Workings of a GLCD

Discussion in 'Embedded Systems and Microcontrollers' started by Utku, Dec 15, 2014.

  1. Utku

    Thread Starter New Member

    Dec 14, 2014
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    Hello,

    I am trying to use a GLCD for my project. Looking at the module's and its drivers' datasheets, some questions have formed in my mind. The links to datasheets are as follows:

    Link for the datasheet of the GLCD module.
    Link for the datasheet of the GLCD module's segment drivers.
    Link for the datasheet of the GLCD module's com driver.

    My questions are a bit lengthy but if you could have time to answer them, I would be very very grateful. So if you would excuse, my questions are as follows:

    1) First of all, why aren't pin numbers of the drivers shown at the block diagram at p.10 of the LCD module's datasheet? Also, not every signal's name is shown as well. Am I supposed to be able to understand how the module works without knowing which signal goes to where in the module?

    2) In the display module's block diagram (at p.10 of the module's datasheet), CS1 and CS2 are connected to their respective segment drivers. Also, there are 8+5 pins connected to each segment driver from the MPU. On the other hand, in the application circuit given in p.20 of the NT7108C datasheet, all CS1B, CS2B and CS3 signals are connected to all segment drivers. Furthermore, there are 8+7 pins connected to each segment driver from the MPU, instead of 8+5 pins. Now what is the meaning of this? Where are the remaining 2 pins connected from in the display module's diagram? Also, why aren't CS1 and CS2 connected to both segment drivers in module's diagram, unlike the application circuit given in p.20 of NT7108C?

    3) In the p.6 of the datasheet of NT7108C, pins; CS1B, CS2B and CS3 are defined as follows:

    "Chip selection
    In order to interface data for input or output, the terminals have to be CS1B=L, CS2B=L, and CS3=H."

    and throughout the entire document, only that given combination of CS1B, CS2B and CS3 is mentioned. My question is: If only a single combination is being used, why are there 3 pins provided for a single task, instead of just 1?

    4) Another point is, I couldn't figure out how am I supposed to connect the GLCD module to my MCU, an ATmega32. I heard that conventionally, SPI is used to connect peripherals to an MCU, but thing is, SPI uses serial connection and the GLCD module that I use has a parallel port for data transfer. So I am a bit confused here also.

    5) My last question is, I came across a tutorial on this page about the use of the GLCD. They put an architecture diagram (named: "GLCD pages") in the website and it explains the form of the architecture very well. My question is, how were they able to understand that architecture is in that way? If that's by looking at the datasheets, could you please underline the places in the datasheets that helped them coming with that architecture diagram? If the sources were not the datasheets, but the experiments they have performed using the module, then my question is: Are there many cases where datasheets of components does not provide enough information and hence, one needs to understand the architecture by conducting experiments, rather then by thoroughly reading the provided datasheets?

    I realize that the questions I asked have been lengthy but if you could have time to explain the answers of these questions, I would be really grateful. Thank you very much in advance.

    Sincerely
     
    Last edited: Dec 15, 2014
  2. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
    2,507
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    hi,
    I assume that you are going to buy the GLCD module.? This has the drivers on board.

    If so, Page section 7. Interface function are the parallel pin connections for the module.

    Page section 10, Display Control function are the program control bytes for the module.

    E
     
  3. Utku

    Thread Starter New Member

    Dec 14, 2014
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    Hi eric,

    Thanks for the reply. Actually I have the module. Thing is, I am trying to understand how the module works internally. That is the reason for my questions; 1-5.

    Regards
     
  4. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
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    you can only use the signal lines that are actually provided externally.

    how am I supposed to connect the GLCD module to my MCU, an ATmega32

    See 7. Interface pin functions. Its not SPI.

    I heard that conventionally, SPI is used to connect peripherals to an MCU

    That's not true its just one convention, not the only one.

    These GLCDs are pretty standard and not difficult to use.
     
  5. Utku

    Thread Starter New Member

    Dec 14, 2014
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    Thanks takao. Yes, actually most of the questions I asked are not directly about using the module but about understanding how it works internally. For example, I can't understand why the block diagram at p.10 of the LCD module's datasheet does not contain the pin numbers on the driver ICs? Is it because the module manufacturer does not want to disclose the details of the module, or is it simply omitted erroneously?
     
  6. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,699
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    The driver IC's are circuit on board (COB) and don't have pins. Therefore, no pin numbers. There could be several reasons why the IC/COB access traces, test points, and GLCD schematic are not given. It could be as simple as the manufacturer didn't feel that information would be useful to retail customers.

    That driver (NT7108C) is likely very similar to the Samsung KS0108 (http://www.techtoys.com.hk/Displays/JHD12864J/ks0108.pdf). The NT7107 is probably analogous to the Samsung KS0107.

    John
     
  7. Utku

    Thread Starter New Member

    Dec 14, 2014
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    I see. Thanks to everybody for your kind attention.

    Regards
     
  8. takao21203

    Distinguished Member

    Apr 28, 2012
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    There are often uncertainities or vague expressions in these datasheets. I have seen quite a few with erroneous english so you'd have a hard time to understand it at all.

    Actually the chips have bump pads but they are microscopic, and there are many, some 100s.
    Its incorrect not all 128x64 are COG (chip on glass), some smaller new kinds are, but theres also a kind with epoxy blob chips, and rubber zebrastrip connectors.

    128x64 is not as much a standard as the character Hitachi kind, but almost, so the parallel kind has the same number of pins, same signals, there could be minor variation, but its all similar.
     
  9. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    While 128x64 is not as much a standard for discrete pixel LCD drivers 64x64 IS a standard, which is why there are two controllers inside for one display.

    You talk to each one in turn by the CS lines.

    One thing to be careful of in these controllers have an automatic adderess increment upon each read or write. For my uses it would have been better for this feature to simply not exist as I had to set the address over and over as it is frequently necessary to read then write each memory byte, and both operations cause an address increment.
     
  10. vishal12345

    New Member

    Dec 16, 2014
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