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I have decided to use an LCD display for my project. In order to learn how to use one, I have consulted its and its drivers' datasheets. Here are the links for them:

Link for the LCD display's datasheet: WDG0151-TMI-V#N00.

Link for the LCD display's segment drivers' datasheet: NT7108C.

Link for the LCD display's com driver's datasheet: NT7107C.

If you would excuse, I would like to ask a couple of questions regarding them.

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

2) Another puzzling point is as follows: In the p.10 of the LCD display's datasheet, there is a block diagram. In that diagram, there are 8+6 lines connected to the MPU. Also, there is an application circuit provided in p.20 of LCD display's segment drivers' datasheet. In the application circuit, there are 8+7 lines connected to the MPU. Now what does that mean?

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) As my last question, in this page, there is an application provided using the same LCD display. In that page, there is a figure given which explains how the display is structured. My question is: How are the authors of the page were able to come up with that figure? More precisely, which points in the datasheets helped the authors of the page to come up with that figure?

Thank you very much in advance.

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This answer is a very general answer to interfacing LCD modules, but looking at the datasheets you provide, it's generally on topic. First you must realize that the LCD module and the LCD driver IC are two separate things. The LCD module manufacturer chooses a driver IC and designs a PCB which holds the driver IC, the LCD glass and most of the surrounding passives that are needed.

The manufacturer then decides which interface pins of the driver IC are brought out to the pin connector of the LCD module. Often a module has an initial customer (often a mobile phone maker) who defines what signals he wants to use to control the LCD. If the mobile phone maker doesn't need some signal, it's often left out to save space on the connector and more importantly on the mobile phone's PCB.

The LCD module maker then makes a "datasheet" of the LCD module, which consists of a mechanical drawing, test acceptance criteria, interface pin listing and the name of the driver IC. Often some pages from the driver IC's datasheet are copied to the module datasheet to make it easier for the reader to get a general idea about how to use the module without having to look into the driver IC datasheet (enough to get an idea if the module might be suitable to a project or not). But beware - the LCD module datasheets are often made from some previous module datasheets .doc file with minimal editing and they sometimes contain even erroneous information that has been left there by accident.

The LCD driver ICs tend to have a fairly established set of digital IO buses that they use: 8-bit or 9-bit 8080-style and/or 6800-style parallel buses (8080 style has separate /RD and /WR signals while the 6800 style has R/W and enable) and 16, 18 or 24 bit parallel bus options as well as an SPI bus option. Any interface mode selection bits that are not needed for the configuration that is brought out to the module's pin connector are left out. Sometimes there are places for pull-up/pull-down resistors on the LCD module's (flexible) PCB that you can tweak - the manufacturer might make the same module in two different configurations and solder the pull-up resistors accordingly differently in manufacturing.

Compared to a lot of modules I've seen you seem to have a lot of information of the module. I've often had to guess a lot of the interface to fill in the missing pieces the manufacturer has left out. Often the LCD modules you find are from manufacturers that are commisioned to make second sources (clones) of existing LCD module types and the original customer just uses the previously existing datasheet - in this case the information from the second module maker might be quite sparse indeed.


Answers

  1. The pin numbers are not needed for the block diagram. Leaving them out allows the module manufacturer to reuse the same block diagram in different products that have different pinouts. The pin numbers can be found in the top-right corner of the mechanical drawing in the previous page (page 9).

  2. CS3 is missing from the module's interface. It means that CS3 is not brought from the driver IC to the 20-pin connector of the module. Thus you won't be able to use the pin CS3, you must accept whatever connection is made to the driver's pin CS3 in the module's PCB. Also "RS" is renamed to "D/I" in the module's connector.

  3. A minute ago I thought that "It's to give you more freedom. For example let's consider that you are driving two LCD modules with a 8080 style microprocessor bus. You would connect the bus to the LCD normally, using CS1 and the other data connections. Then additionally you would control the CS2 of both modules individually by software. That way you can select which LCD of the two actually receives your operations.", which would be true generally. But upon closer look at the module, I realize that the module contains two driver ICs, and CS1 goes to one of the active low chip selects of the first driver IC and CS2 goes to the other driver IC. The remaining chip selects of the drivers are permanently connected high or low on the module's PCB.

  4. There might be an application note somewhere that we don't know anything about which holds this information, but it's actually quite easy (and often necessary) to get this info by experimentation. You start by clearing the display and then write some data to the display in a loop with some delays and look visually where the dots start appearing and in which order. It helps that there usually aren't so many different ways to connect the driver that would make any sense - different modules are usually quite similar and as you gain some experience, it gets easy to find it out.

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  • \$\begingroup\$ Thanks but what are the answers of my questions 1-4? Do you that mean that it is not possible to provide answers to those questions with the amount of information existing in the datasheets? \$\endgroup\$ – Utku Dec 14 '14 at 9:27
  • \$\begingroup\$ No, I'm sure the info can be found. Ok, give me a minute to revise my answer \$\endgroup\$ – PkP Dec 14 '14 at 9:37
  • \$\begingroup\$ 1) But does it really makes sense to provide a block diagram without indicating pin numbers and signal names? Because in that case, I cannot know which signal connects to where and hence, how am I supposed to understand how the module works? \$\endgroup\$ – Utku Dec 14 '14 at 10:15
  • \$\begingroup\$ 2) Similar problem persists here as well. For example, there are no such pin as CS1 or CS2 in the datasheet of NT7108C. There are; CS1B, CS2B and CS3. I guess that I am supposed to guess that CS1 corresponds to CS1B and CS2 corresponds to CS2B. But in that case, what is connected to CS3? Or is it irrelevant to know what is connected to CS3? \$\endgroup\$ – Utku Dec 14 '14 at 10:19
  • \$\begingroup\$ 3) No. If I am not mistaken, all CS1B, CS2B and CS3 goes to all driver ICs. Also, what is the purpose of providing multiple chip select pins to a single driver IC? \$\endgroup\$ – Utku Dec 14 '14 at 10:26

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