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The pipeline lamp, digital tube and LED lattice we talked about before are mostly LED equipment. In this lesson, let's learn about LCD display equipment-1602 LCD. Who is big, the first line usually shows 16 small black blocks, and the second line shows nothing is the 1602 liquid crystal. Have you noticed it a long time ago?

Everyone to learn these electronic devices, the mind should gradually form a kind of understanding, whether it is our single-chip microcomputer, still 74HC138, and even Triode, and so on, most of them do not have a data manual. Whether it is designing the circuit or writing the program, the data manual of the device is our best reference material, so if we come to study 1602 tomorrow, we will look at its data manual at the beginning. The manual can be found on the Internet. I will only focus on the manual when I talk about it here.

First of all, let's look at a table of secondary skill parameters, as shown in Table 12-3.

Table 12-3 1602 liquid crystal secondary skill parameters

Display capacity 16 x 2 character chip task voltage 4.5V 5.5V task current 2.0mA (5.0V) module optimal task voltage 5.0V character size 2.95 x 4.35mm (width times height)

1602 LCD, we can see its display capacity from its name, that is, it can display 2 lines of 16-character LCD. Its task voltage is 4.5V~5.5V, about which we design the circuit directly according to the 5V piecemeal design, but guarantee that our 5V piecemeal minimum should not be less than 4.5V. In the 5V task voltage to measure its task current is 2mA, everyone pay attention to, this 2mA only refers to LCD, and its yellow and green backlight is mostly made of LED, so the power consumption will not be too small, 10 or 20 Ma still have.

1602 LCD has a total of 16 pins, and the function of each pin can be obtained in its data manual. These basic information must be read clearly before we design the circuit and write the code, as shown in Table 12-4.

Table 12-4 1602 LCD pin function

Numbering symbol pin clarifying numbering symbol pin clarifying 1VSS power source 9D2Data I/O2VDD power positive 10D3Data I/O3VL liquid crystal display bias signal 11D4Data I/O4RS data / edict selector 12D5Data I/O5R/W read / write selector 13D6Data I/O6E enable signal 14D7Data I/O7D0Data I/O15BLA backlight positive 8D1Data I/O16BLK backlight negative

LCD power supply 1 foot 2 feet and backlight power supply 15 feet 16 feet, needless to say, normal connection is OK.

3 feet is called LCD bias signal, everyone noticed whether the small black block or not, when we want to display a character, some black spots display, some black spots can not be displayed, so we can complete the characters we want. Our 3-foot is used to adjust the illuminance between the displayed black spots and the undisplayed ones. If we adjust the illuminance, we can make our display clearer. When stopping the circuit design experiment, the usual method is to connect a potentiometer to this pin, that is, the sliding rheostat we learned in junior high school. Adjust the voltage of the 3-pin by adjusting the voltage value of the potentiometer. When the product is consumed in bulk, we can adjust this value directly with a complex circuit, just as on our board, we directly use an 18-euro pull-down resistor. Some 1602 pull-down resistors on the market are also comparable appropriate values of about 1 to 1.5K.

The 4-foot is the data command selector. With regard to LCD, sometimes we have to send some edicts to let it complete some of the forms we want, and sometimes we have to send it some data to show it. LCD will go through this pin to distinguish whether it is accepted by imperial edict or data. This pin is connected to ADDR0 and connected with P1.0 through jumper cap. Everyone pay attention to learn to read the manual and see the pin description: data / edict selector, followed by parentheses (High L). What he means is that when the pin is H (Low) high, it is data, when the pin is L (Low) low, it is imperial decree.

The use of 5-foot is similar to that of 4-foot, and the function is read-write selector. We can either write to the LCD data or edict, or we can read the data or shape outside the LCD, which is to master this pin. Because there is RAM on the outside of LCD itself, in practice, the edict or data we send to LCD, LCD requirements are first kept in the cache, and then written to the external memory or RAM, which requires a certain amount of time. So before we stop reading and writing, first read the liquid crystal after the shape, is not in the "busy", if not busy, we can read and write data, if in the "busy", we need to wait for the liquid crystal busy, and then stop the operation. Reading form is commonly used, but the place where I have come into contact with liquid crystal data has not been used much, everyone can understand this function. This pin is connected to the ADDR1 and connected with the P1.1 through the jumper cap.

The 6-foot is the enable signal, which is the crux of the problem. The reading and writing orders and data of LCD depend on it to read and write normally. We will talk about how to use this pin later. This pin is connected to the ENLCD through the jumper cap, and the jumper of this position is designed to switch with another 12864 LCD.

7 to 14 pins are 8 data pins, through which we read and write data and edicts. We all received the P0 port. Let's take a look at the reason diagram of the 1602 interface on the opening board, as shown in figure 12-1.

Figure 12-1 1602 LCD interface reason diagram

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