Fullscreen HTML5Med Res (??MB)HTML4

Alphan11meric LCD Demonstration Board Using an alphanumeric LCD panel is not as hard as you may have thought. In this article, we show you how to interface one to a PC printer port. By DARREN YATES Over the last few years, the cost of alphanumeric displays has dropped dramatically. That's hardly surprising, considering they are being used increasingly in consumer goods as the push continues for "smart" appliances. Most of these displays are controlled. by _microprocessors and are designed to make complicated equipment easier to operate. Items such as microwave ovens, fax machines, CD 64 SILICON CHIP players and car stereos now use alphanumeric panels to display options and commands to help the user achieve the desired result. Alphanumeric LCDs are available in many shapes and sizes but one of the most cost-effective types is the 16 character x 2 line display that's used here. It requires only 11 connections - eight bits for data (which can be reduced to four if necessary) and three lines for control. It runs off a SV DC supply and sells for just $35, making it perfect micro- . processor-controlled projects. Circuit details The LCD module contains two microprocessors and that's about all there is to tell. These can be easily described as the two black blobs on the back of the PC board. Apart from the display itself there's nothing else, it's that compact. · Fig.1 sh_o ws the simple circuitry that goes with the display. As you can see, it consists of a power supply which uses a 78L05 lO0mA 3-terminal regulator to derive a regulated SV rail. The power is derived from a 9V 300mA plugpack, while D1 provides reverse polarity protection. Since the display requires only about lmA of current, this arrangement is more than adequate. The display contrast is adjusted by means of a 10k.Q trim pot which feeds a voltage into pin 3 of the display. Apart from that, all you need is a male-to-male DB25 cable to connect the display to the PC. D1 1N4004 9VDC 300mA _ __ PLUG-PACK VR1 10k Programming Normally, you would expect to see these displays being driven from a dedicated microcontroller but it's quite easy to get the display to work from your PC's parallel printer port. That's because the display can be easily controlled by programming port A for the eight data bits and port C for the three control lines (note: port A and port C are both part of the one parallel port). One thing that should be noted with the printer ports is that the addresses we've used for port A are 0378 hex (888 decimal) and for port C, 03 7 A hex (890 decimal). All the pins for port A are noninverted; ie, if you set a particular bit to "1", then that bit goes high. However, for Port C, we have used the lower three bits and the first two qie inverted; ie, to set them high, you need to set that bit to "0", not "1". The computer program takes care of all this and you don't need to know very much about computing to get the display to work. For those who are interested in how to program it, the computer program contains documentation which shows the programming sequence. PARALLEL PRINTER PORT (2) o o o - - - - - " - 1 1 vcc VO (3) 0 1 0 - - - - - a t 9 (4) 0 2 0 - - - - -at 2 ROW x16 CHARACTER ALPHANUMERIC DISPLAY AL TRONICS CAT.Z-7299 (5) D 3 0 - - - - - '10LI 11 (6) D 4 o - - - - ~-'1 (7) D5o-----'12at 13 (8) D 6 0 - - - - - - - 'at (9) D 7 0 - - - - - - - ' -14af RS R/W 4 5 E GND 6 (1) S T R o - - - - - - - - - ' (14) A F O - - - - - - - - _ _ . (16) 1 0 - - - - - - - - - - - ' (19-21) GND°"l- 0 I G0 VIEWED FROM BELOW ALPHANUMERIC DISPLAY DEMONSTRATION BOARD Fig.1: the circuit consists of the alphanumeric display module plus a power supply which uses a 78L05 lOOmA 3-terminal regulator to derive a regulated +5V rail. The eight display data lines interface to port A of the parallel printer port, while the three control lines interface to port C. lr, ~·,25-PIN D CONNECTOR Instructions OK, let's get down to the business end of things. The first thing to look at is the three control inputs to the display. They are REGISTER SELECT (pin 4), READ/WRITE SELECT (pin 5) and OPERATION ENABLE (pin 6). The REGISTER SELECT input controls whether you are writing an instruction to the on-board microprocessor (input set to O), or writing data to be displayed on the screen (input set to 1). The on-board microprocessor allows for quite a few different effects, such as shifting characters, scrolling the display left or right, and defining your own characters. We'll look more closely at these special effects later. The READ/WRITE select input allows you to read the current address counter and the busy flag status. They are not often used and are not re- Fig.2: install the links (shown dotted) on the PC board before mounting any of the other parts. The alphanumeric display is connected to the PC board using a right angle pin header which is soldered to the underside of the module. quired to operate the display. The OPERATION ENABLE input is very much like the ENTER key on your keyboard. This pin must be taken high and then low again before the instruction or data is entered in (ie, the operation takes place on the negative going edge of the enable signal). Table 1 is a quick reference chart of the instructions and the corresponding code. By using the printer port, you can program the display in just about any language you like, as long as it has an instruction which allows you to send data to the printer port registers. Let's start by turning the display on. To do this, we initially set port A MAY 1993 65 RS Clear Display 0 0 0 0 0 0 0 0 Cursor Home 0 0 0 0 0 0 0 0 Entry Mode Set 0 Notes R/W 087 086 085 084 083 082 081 080 Parameter 0 0 0 0 0 0 * 1/D 0 DB1 =1: Increment DB1=0: Decrement DB0= 1: Display not shifted s DB0=0: Display shifted Display on/off 0 0 0 0 0 Cursor/ Display Shift 0 0 0 0 0 System Set 0 0 0 0 Set CGRAM Address 0 0 0 Set DDRAM Address 0 0 Read Busy Flag/Address Counter 0 D C B DB2= 1: Display on; DB2=0: Display off DB1 =1: Cursor on; DB1 =0: Cursor off DB0=1: Blinking on; DB0=0: Blinking off S/C R/L * * DB3=1: Shifts display one character DB2= 1: Right shift; DB2=0: Left shift N F * * 0 DB4=1: 8 bits; DB4=0: 4 bits Write Data DL BF The maximum address length is 64 Add The maximum address length is 80 AC DB7 =1: Busy (instruction not accepted) DB7=0: Ready (instruction accepted) Read Data to 12, which is DB3 and DEZ set high. Port C is then set to 7 and then to 3 see Table 1. Because the first two bits of port C are inverted, we need to set them to 1 to get O's at the output. Setting this port to 7 pulls the enable input of the display high and then setting it to 3 0 0--0 Acg Write Data 0 Read Data 0 DB3=1: 2-line display (1/16 duty cycle) DB3=0: 1-line display pulls it low again. If we are using DOS 5.0's QBasic programming language, the code looks like this: OUT 888,12 OUT 890,7 OUT 890,3 If you try this on a 486 machine, 0 :I 0 PC - Alpho.nuMerlc dlsplo.y boo.rd 07106931 0 66 a '--=~-=--=-=__,fllnmm SILICO N CHIP you might find that the change from high to low produced by the last two instructions might be too fast for the microprocessor, so a small delay should added in; eg, by using a FOR .. .NEXT loop. The display initially boots up in an 8-bit data 1-line mode, so we can start entering characters to be displayed o'n the screen almost immediately. One of the best features of this display is that it accepts standard ASCII code. This makes it very simple and versatile to program as it matches the code used in your PC. For example, let's assume that we want the words SILICON CHIP to appear on the top 0 0 Fig.3: check your PC board for etching de(ects by comparing it with this full-size pattern before installing any of the parts. The board measures 128 x 77mm (code 07106931). PARTS LIST Alphanumeric Display Board Demo Software Copyright 1993 Silicon Chip Publications 1 PC board, code 07106931, 128 x 77mm 1 9VDC 300mA plugpack 1 DB25 female right-angle PCB mount connector 1 3.5mm PCB mount socket 1 single way right-angle pin header 2 5mm untapped spacers 2 3mm x 9mm machine screws & nuts 4 rubber feet 1 10kQ trimpot 1 demonstration program (LCD.EXE) - see below COMMANDS (1) Scroll the display right (2) Scroll the display left (3) Enter in text (4) Create a character (5) Turn cursor offi'on (6) Enter in custom character (7) Move cursor (8) Clear display and cursor home (q) quit Command: Fig.4: this is the opening menu of the demonstration program LCD.EXE. By selecting the appropriate number & pressing <enter>, you can enter in text, scroll the display left or right, & create custom characters. Capacitors 1 100µF 16VW electrolytic 1 33µF 16VW electrolytic 1 0.1 µF 63VW MKT polyester Alphanumeric Display Board Demo Software Copyright 1993 Silicon Chip Publications 12:-145 1 Semiconductors 1 2 .row x 16 character alphanumeric display (Altronics Cat. Z-7299) 1 78L05 5VDC 100mA regulator 1 1N4004 diode (01) Where to buy the software The demonstration program LCD.EXE & the source code LCD.BAS can be obtained by sending $10 plus a formatted 5.25-inch or 3.5-inch floppy disc to : SILICON CHIP, PO Box 139, Collaroy Beach , NSW 2097. ♦ 2 3 4 5 6 7 B 0 Move cursor using arrow keys & press <ENTER> to turn the point on/off Press ESC to end editing Fig.5: this on-screen display is brought up by entering <4> <enter> at the opening menu. It allows you to create custom characters by moving the cursor to a desired point using the arrow keys & then pressing <enter> to turn that point on or off. line. The ASCII code for an "S" is either 83 decimal or 53 hex. We don't have to program in hex so we can just use the decimal code. To display the "S", the code would look like this: OUT 888,83 OUT 890,6 FORD = 1 TO 10: NEXT D OUT 890,2 Notice the difference between this and the last section of code. Because we are now entering data and not instructions into the display, the REG- !STER SELECT line is taken high (remember the inversion). The FOR.NEXT loop adds in a delay to make sure that all lines have settled into their final state before w e enter the code. The next letter to be entered is "I". This has an ASCII code of 73 and is entered in exactly the same manner as the "S" except that we now substitute 7~. for 83. Each character code is entered into one of 80 memory locations to give two lines of 40 characters. Because only 16 characters per line can be displayed at any one time, there is an instruction which allows us to scroll the display to either the left or the right. The code for shifting the display one character to the right is 28, while the code for shifting it to the left is 24 - see Table 1. For this project, the basic rule is that if you're entering a command, then you must toggle port C (that's address 890) to 7 and then back to 3. If you're entering data into the display, you have to toggle it to 6 and then back to 2. Each time you execute a shift command, the display is shifted one character in that direction. So in order to scroll the display, you have to enter the code in as many times as you wish to move characters. If you do it indefiMA Y 1993 67 Alphanumeric Display Board Demo Software Copyright 1993 Silicon Chip Publications Alphanumeric LCD Demo Board * * note: first 16 characters only shown. * * press 'x' at line 1 to quit * * Enter in data to be displayed on line 1: Alphanumeric Enter in data to be displayed on line 2: LCD Demo Board Text is entered by pressing <3> <enter> at the opening menu & then typing in the required message. Note that the on-screen text window only shows the first 16 characters of each line, although up to 40 characters can be entered. Alphanumeric Display Board Demo Software Copyright 1993 Silicon Chip Publications COMMANDS (1) Scroll the display right (2) Scroll the display left (4) (5) (6) (7) (8) Create a character Turn cursor off/on Enter in custom character Move cursor Clear display and cursor home Alphanumeric LCD Demo Board (q) quit Command: which of the five dots in that row are to be on and off. Each bit that is set to 1 represents a dot that is on. Again, each row data entry must be followed by port C being fed with 6 and 2 to enter it in. This means that it takes a series of eight instruction sets to create one character. This character is then stored in memory and can be recalled for display by entering O through to 7 for each of the eight characters; ie, OUT 888,0 for character 1; OUT 888,1 for character 2, etc. Construction All of the components for the Alphanumeric Display Demo Board are installed a PC board coded 07106931 and measuring 128 x 77mm. Before you begin construction, make sure that all the tracks on the PC board are OK and that there aren't any defects such as shorts or breaks. If you find any, use a small artwork knife or a small blob of solder where appropriate to fix the problem. The first job is to solder a 16-way right-angle pin header to the edge connector of the display board - see photo. This done, install the 3.5mm socket, the 3-terminal regulator and other components as shown in Fig.2. The PC-mount DB25 socket can then be installed on the board, followed by the LCD module itself. The top of the LCD module is supported on two 5mm spacers and secured using machine screws and nuts. Use the mounting holes at the top of the module as guides when drilling the mounting holes in the PC board. Software Pressing the <enter> key after the second line of text has been entered returns you to the opening menu. The text can be cleared by pressing <8> <enter>. nitely, then the display will scroll across the screen continuously. Character generation The display has a character set which contains 240 different characters but for those who want to "roll their own", there are eight custom characters which can be programmed into the display. To make this easy, our demonstration program (LCD.EXE) has a character generation table built in which allows you to turn any one of the 8 x 5 dots in the character on or off. The 68 SILICON CHIP program then enters the data into one of the eight special character RAMs. To explain briefly how this works, if you refer to Table 1 you will see the instruction SET CGRAM ADDRESS. After bit DB6 has been set high, you can set the CGRAM address counter to · one of 64 addresses. The first eight addresses correspond to the eight rows of the first character, the next eight addresses to the eight rows of the second character, and so on, up to a maximum of eight characters. Once a character address has been set, the data then entered represents As mentioned earlier, a demonstration program (LCD.EXE) plus the source code (LCD.BAS) to go with this project are available from SILICON CHIP (see parts list for details). LCD.EXE allows you to produce all the effects described in this article and is started by typing LCD<enter>. The main command screen is then displayed and this provides a menu of all the possible commands. The software is very straightforward to run and requires no knowledge of how the LCD panel works to get it running. The source code provided runs under DOS 5.0's QBasic. Its main aim is to give experienced programmers a chance to customise the software to suit their own requirements. SC