SLCD1-IC Serial LCD Processor

Transcription

1 SLCD1-IC Serial LCD Processor Diagram 1: LCD Pin 13 LCD Pin LCD Pin 12 LCD Pin 11 N/C MHz Osc DC MHz Osc Ground 5 14 DC Serial Input True/Inverted LCD Pin 6 LCD Pin 4 Baud Rate (See Table 2) 8 11 LCD Pin 2 LCD B/L 9 10 Baud Rate (See Table 2) Introduction: The SLCD1-IC is an LCD interface processor that accepts standard Serial data as input and sends that data to a character LCD via 4-bit parallel bus. The SLCD1-IC is housed in a standard.3 wide, 18 pin microprocessor package. The purpose of the SLCD1-IC is to allow the user to communicate with a character LCD via one I/O pin. It is intended for use with character LCD s with one to four lines, which use the extremely popular Hitachi HD44780 controller or equivalent. The Serial transmission is 8N1 (8 data bits, no parity, 1 stop bit). True/Inverted Modes: The SLCD1-IC does not include an RS-232 voltage level converter. This assumes that the input voltage on pin 6 (Serial Input) is TTL levels, which are 0V to. However, due to the excellent I/O capabilities of the PIC16F628A (which is the microprocessor that is used to create the SLCD1-IC), the SLCD1-IC can usually interface to a PC (RS-232 voltage levels) by setting pin 7 to 0V (Inverted). In summary, here are the three basic situations concerning the True/Inverted modes. 1. Connecting SLCD1-IC to a device producing TTL voltage levels: Select the appropriate baud rate. Next, you can use either True or Inverted mode. Each will work fine. 2. Connecting SLCD1-IC to a PC or some other RS-232 voltage level device for RS-232- compatibility: Select the appropriate baud rate. Next, set to Inverted mode. This will usually allow for proper communications. However, certain Serial ports on PC may not sense the signal. However, it should be noted that this will not damage the PC Serial port or the SLCD1-IC, as long as the 22K ohm resistor is used, as shown in Diagram Connecting the SLCD1-IC to a PC or some other RS-232 voltage level device for RS-232- compliance: Select the appropriate baud rate. Next, set to True mode. Finally, an RS-232 voltage level IC, such as Maxim IC s ( MAX232 should be used to send the input signal into pin 6 of the SLCD1-IC. This will guarantee that the SLCD1-IC will always work with any RS-232 device. Note: We plan on releasing an RS-232-compliant Serial LCD controller in the future. Therefore, if it is necessary for you to have RS-232-compliance, please contact us for the status of the appropriate part.

2 Pin Assignments: Table 2 shows the pin assignments for the SLCD1-IC. Pin 1: Pin 13 of the LCD. This is one of the four data lines that must be connected from the SLCD1-IC to the LCD. Pin 2: Pin 14 of the LCD. This is one of the four data lines that must be connected from the SLCD1-IC to the LCD. Pin 3: Not Connected Pin 4: This pin should be pulled up to with a 4.7K ohm resistor. It is the reset pin for the SLCD1-IC. When it is pulled high, the SLCD1-IC will be active. When it is pulled low and then high, it will reset. Pin 5: This pin should always be connected to ground (0V DC). It is the system ground for the SLCD1-IC. Pin 6: This is the input pin for the Serial data and commands. Pin 7: This is the polarity pin. This pin determines if the Serial data being received by the SLCD1-IC is True or Inverted. Pin 8: This is one of the two pins that determine the baud rate of the data that will be sent to the SLCD1-IC. See Table 2 for valid baud rates. Pin 9: LCD backlighting pin. This pin will be raised to when the special command $10 followed by $03 is received by the SLCD1-IC. The pin will be lowered to Ground when the special command $10 followed by $04 is received by the SLCD1 - IC. If LCD backlighting is not available on the LCD or if it is not needed, this pin can be used as a general-purpose output pin capable of sinking 25mA. If the load being controlled by this pin is greater than 25mA, then a transistor should be wired between this pin and the load. Pin 10: This is one of the two pins that determine the baud rate of the data that will be sent to the SLCD1-IC. See Table 2 for valid baud rates. Pin 11: LCD pin 2. This is the power pin of the LCD. The LCD can be turned off in order to lower the current draw of the system by sending the special command $10 followed by $02. The LCD can be turned on in by sending the special command $10 followed by $01. The LCD is turned on when the system is turned on or is reset. Turning the power on/off on the LCD can be especially important when the system is being powered by batteries. Pin 12: LCD pin 4. This is the RS pin of the LCD. Pin 13: LCD pin 6. This is the E pin of the LCD. Pin 14: This pin should always be connected to DC. This is the power supply for the SLCD1-IC. Pin 15: This pin should always be connected to one of the two pins on the 8 MHz parallel cut crystal. Pin 16: This pin should always be connected to one of the two pins on the 8 MHz parallel cut crystal. Pin 17: LCD pin 11. This is one of the four data lines that must be connected from the SLCD1-IC to the LCD. Pin 18: LCD pin 12. This is one of the four data lines that must be connected from the SLCD1-IC to the LCD. Baud Rate: Table 1 Table 2 shows the settings of pin 8 in order to set the baud rate. Baud Rate Pin 8 Pin V 0 V V 5 V V 0 V V 5 V Table 2

3 Sample Connection Diagram: 8 MHz 0.1uF SLCD1- IC N/C 220 4K7 From Serial Output Source 10K 1K 1 16 Diagram 2 NOTE: Diagram 2 is the suggested schematic for the SLCD1-IC. It is also the exact circuit used in our SLCD1-PCB.

4 Sending Printable Characters: Once the user matches the baud rate and polarity via the three jumpers, sending data to the SLCD1- IC is straightforward. Simply send the string of characters that should be displayed. Of course, the syntax for the Serial command is different for each language. We will use the PicBasic (www. melabs.com) SerOut command in our examples. To send the word, hello, the command would be as follows: SerOut opin, mode, [ hello ] where opin is the designated output pin of the microprocessor Mode is the code that specifies the baud rate and polarity in PicBasic Again, don t worry too much about the PicBasic syntax. Just remember that you can simply send the characters that should be displayed. Sending Instructions: Sending printable characters was described in the previous section. However, the user can also send special characters that are interpreted by the SLCD1-IC as instructions. The special instructions that are described in this section can be broken down into two types of instructions. First, there are the commands of the Hitatchi HD44780 controller. These commands are executed by sending hexadecimal value, FE (which equals decimal 254 and binary ), followed by the character that represents the command. Some of the most common commands of the Hitatchi HD44780 are listed in Table 3. In brief, you can send any HD44780 command into the SLCD1-IC and it will then pass that command to the HD44780 controller on the LCD. The examples shown below are only a sample of these commands that can be sent to the LCD. Please be sure to read the datasheet of the HD44780 and LCD that COMMAND OPERATION is being used in order to take full advantage of the $FE followed by $01 Clear display (and return home) commands. Second, there are the commands that we included in the SLCD1-IC. These commands are executed by sending hexadecimal 10 (which equals decimal 16 and binary 10000), followed by the character that represents the command. All of these commands are listed in Table $FE followed by $02 Return home $FE followed by $0C Turn cursor off $FE followed by $0E Turn underline cursor on $FE followed by $0F Turn blinking block cursor on $FE followed by $10 Move cursor one position to the left $FE followed by $14 Move cursor one position to the right $FE followed by $80 Movecursor to the beginning of the first line As described above, to send printable characters to the LCD, the user $FE followed by $C0 Move cursor to the beginning of the second line can simply send the data into pin 6 $FE followed by $94 Move cursor to the beginning of the third line of the SLCD1-IC. Sending commands is not much different than $FE followed by $D4 Move cursor to the beginning of the fourth line sending printable characters. The Table 3: Common Hitatchi HD44780 Controller Commands first thing to know is that the Hitachi HD44780 requires that $FE must be sent immediately before the command. This allows the LCD controller to distinguish between printable characters and instructions.

5 NOTE: The dollar sign acknowledges that the following number is in hexadecimal format. The FE is 254 in decimal. The HD44780 will accept either $FE or decimal 254 or even the binary or octal equivalent. However, the hexadecimal format is usually used. NOTE: Make note that the commands in Table 3 are in hexadecimal format. We will go through a few examples using some of these commands. Then, later in this document, we will describe how to take commands in binary format and build commands in hexadecimal format for use with the SLCD1-IC. Example #1: Now that we have a list of commonly-used Hitatchi HD44780 controller commands in hexadecimal format in Table 3, let s create an example with one of these commands. In this example, assume we are using a 16x4 display. We will clear the LCD and display the string, First Line on the first line. We will then move the cursor position to the beginning of the third line and display the string, Third Line. Then let s say that we want to clear the screen later in the program and print the string, Second Line on the second line of the display. Again, we will use the PicBasic SerOut command to illustrate this example. SerOut opin, mode, [$FE,$01] : pause 10 SerOut opin, mode, [ First Line ] SerOut opin, mode, [$FE,$94, Third Line ]... SerOut opin, mode, [$FE,$C0, Second Line ] NOTE: Although the three characters $FE is sent, it represents a one-byte character. That is a key point to remember. When sending serial data, you send one character at a time. With the PicBasic syntax, each byte is separated by a comma and strings are enclosed in quotation marks. The quotation marks and commas are not displayed on the LCD. IMPORTANT NOTE: It is necessary to pause the serial transmission when certain special commands are sent. One example is when clearing the display (by sending hexadecimal FE followed by hexadecimal 01). This is necessary to allow the LCD controller to execute the command. That is why there is pause 10 in Example #1. This pauses for 10 milliseconds. Various commands have different execution times. However, 10 ms should be enough of a delay. If you experience problems when sending any commands, try making this delay longer. Example #2: That first example is very useful. However, how can the user display text on a line without starting at the very beginning of the line? For example, let s display the string, Third Line on the third line, but have two spaces before the text. One way to do this is as follows: SerOut opin, mode, [$FE,$94, Third Line ] where there are two spaces before the text. However, another way would be to position the cursor at the third character of the third line and then display the text, without having to put two spaces in the front of the text. Before we show this example, we need to ask question in order to understand how we can do this: What does the $94 actually

6 mean? This is directly related to the address (DDRAM) of that position on the display; however, it is not the actual address. We will now explain, in two steps, how we arrived with the $94 value. The first step will be to reference the memory layout of the LCD which we are using (Diagram 3). The second step will be to take the address found in the first step and reference the table of general binary commands for the HD44780 controller (Table 3). So let s begin. First, we must find the address of the particular positionon the display which we want to set the cursor. This can be done with Diagram 3. Diagram 3 shows the addresses of most character LCD s. You should refer to the datasheet of the LCD which is being used to make sure of the proper memory layout and addresses. However, we will use Diagram 3 for our example. Since, in our example, we are using a 16x4 display, and we want to place a string at the third character of the third line, we need to find the address for that position. Keep in mind that the addresses in this diagram are in hexadecimal format. You will note that the addressis$14 (20 in decimal) So why don t we use $14 instead of $94? That is because we need to complete the second step in the process, which is to refer to Table 5, which is shown below. When positioning the cursor to a particular character position on the screen, the user is actually setting the DDRAM address. Therefore, we must turn our attention to the Set DDRAM Address instruction in Table 3. Bits AC0 through AC6 represent the address, in binary format. In the previous paragraph we found the address to be $14. The binary format for $14 is Therefore, the instruction code is actually in binary format, and $94 in hexadecimal format. That is how the $94 value is derived in Table 5. That is why Table 5 is only a partial list of potential instructions that can be sent to the LCD. NOTE: In Diagram 3 you will notice an RS and R/W column. These columns are included on this table for informational purposes only. The SLCD1-IC will raise and lower the voltage on these pins as needed. However, the following is a short explanation of their duty behind the scenes. The RS column in Table 5 corresponds to the Register Select pin on the LCD. When this pin is high (1), the controller expects the value which will be sent next to be data. When this pin is low (0), the controller expects the value which will be sent next to be an address. The R/W column in Table 5 corresponds to the Read/Write pin on the LCD. When this pin is high (1), a value is being requested from the controller. When this pin is low (0), a value is being sent to the controller. Now that we know how $94 is derived, we can continue with our example of displaying text at the third character position on the third line. This can be done as follows: SerOut opin, mode, [$FE, $96, Third Line ] We can derive the $96 just as we did the $94. Let s explain how the value $96 was derived. We need to find the address of the third character on the third line. We find this value in Diagram 3 to be $16, who s binary equivalent is Therefore, using Table 5, we use the command The hexadecimal equivalent is $96. Example #3: Let s look at another more example. Let s assume that the user wants to move the cursor one position to the right, regardless of the current position. The size of the display and the current position are not needed for this example. It will work the same for all display sizes and all cursor positions. From Table 3, we know that the hexadecimal code to move the cursor to the right is $0E. However, how is it derived? We will need to reference Table 5. We will need to turn our attention to the Cursor or Display Shift command. These examples should illustrate that, although many commonly-used commands are shown in Table 3, many commands can be derived by using Diagram 3 and Table 5.

7 Diagram 3 Example #4: The first three examples described Hitatchi HD44780 controller commands. Next, we will describe a few examples showing how to use the SLCD1-IC commands, which are shown in Table 4. COMMAND OPERATION $10 followed by $01 Turns on power to the LCD. $10 followed by $02 Turns off power to the LCD. $10 followed by $03 Turns on Backlighting to LCD $10 followed by $04 Turns off Backlighting to LCD This example will show how to turn the power off to Table 4: SLCD1-IC Commands the LCD. This is useful when the system is powered via batteries, so that the battery life can be extended when the display is not needed. The following command would turn off the power to the LCD.

8 Instruction RS R/W DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0 Description Clear Display Move Cursor Home On/Off Control Cursor or Display Shift Set CGRAM Address Set DDRAM Address Write Data to RAM Read Data from Ram D C B S/C R/L AC5 AC4 AC3 AC2 AC1 AC0 Set CGRAM address AC6 AC5 AC4 AC3 AC2 AC1 AC0 Set DDRAM address Turn on or off the display (D), cursor (C) and blinking of cursor (B) Set cursor (C) or display (D) shift to right (R) or left (L) 1 0 D7 D6 D5 D4 D3 D2 D1 D0 Write data into LCD RAM (DDRAM / CGRAM) 1 1 D7 D6 D5 D4 D3 D2 D1 D0 Read data from LCD RAM (DDRAM / CGRAM) SerOut opin, mode, [$10, $01] Similarly, to turn the power on to the LCD, you would use: Table 5 SerOut opin, mode, [$10, $02] : pause 100 IMPORTANT NOTE: An important note here is the pause 100 command. The LCD needs a certain amount of time to power up and initialize. A pause of 100 milliseconds should be sufficient. However, if you experience any problems, try to extend this pause value. Example #5: The next example will show how to turn the backlighting of the LCD on. This will only work if the LCD has 16 pins. If it has 14 pins, then you have one of two types of LCDs. First, you may have an LCD that does not have backlighting. Second, you may have an LCD that has backlighting, but it may have a separate Anode (positive) and Cathode (negative) pins, usually on one of the short sides of the display. In this second case, you would have to wire jumper wires from pin 15 of the SLCD1-IC to the Anode pin of the LCD. Similarly, you would have to wire a jumper wire from pin 16 of the SLCD1-IC to the Cathode pin of the LCD. These two jumpers would be needed because pin 15 on the SLCD1-IC is the positive pin for the backlighting and pin 16 on the SLCD1-IC is the negative pin for the backlighting. Now that we have described how the backlighting should be connected to the SLCD1-IC, we will show how to turn the backlighting on and then off. In order to turn the backlighting on (raise the line to ), you would use the following command:

9 SerOut opin, mode, [$10,$01] Then, lets say you want to turn the backlighting to the LCD off, you would use the following command: SerOut opin, mode, [$FE,$02] NOTE: Please note that the syntax of these command examples is PicBASIC, from ME Labs (www. melabs.com). You will need to adjust the syntax to reflect the language which you are using. However, the important point to understand is that the two bytes must be sent to the SLCD1-IC in order for the commands to execute properly. NOTE: If you do not have, or do not need, backlighting, pin 15 can be used as a general-purpose output pin to turn on/off other things such as LEDs or buzzers. However, keep in mind that pin 15 can sink no more than 25mA without an external transistor connected to it. If you attempt to turn on something that draws more than 25mA, it may damage the SLCD1-IC, an would not be covered under the warranty.

10 DB9 and DB25 Interfaces If the SLCD1-IC is being connected to a PC without the use of an RS-232 voltage level converter IC, the user must connect a 22K ohm resistor as shown in Diagram 4, when connecting to a PC. The most common type of serial port connector is the DB9. The DB25 is also popular. Refer to Diagram 4 for the proper pin assignments. Diagram 4 Electrical Characteristics: The SLCD1-IC is designed to be run on regulated DC. Therefore, the system voltage should not be out of the 0V to DC range. Any other voltage can damage the SLCD1-IC and will not be covered under the warranty.

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