Displaying Characters on an LCD Character Module - Hantronix, Inc

Application NoteINC.Crystal Clear and Visibly Superior LCD Modules<strong>Displaying</strong> <strong>Characters</strong> on an LCD Character ModuleI. Introduction:This application note describes a simple technique to display characters from both the internal charactergenerator and user designed characters on an LCD character module.The controlling microcontroller isa Phillips 87C751, a derivitive of the popular Intel 8051. The LCD module is connected to the microcontrollerthrough its I/O ports. It could also be connected directly to the data bus with the addition ofaddress decoding logic.The process of displaying character to this module is divided into three steps. First the module must beinitialized. This sets up the built-in LCD controller chip. Second, some user designed characters areuploaded to the CGRAM. This allows the displaying of up to 8 custom characters in addition to the 192character permanently stored in the module. Lastly, a message consisting of a mix of standard ASCIIcharacters and custom designed characters is displayed on the module.II. Circuit Schematic5VVddGNDP1.0P1.1P1.2P1.3P1.4P1.5P1.6P1.7D0D1D2D3D4D5D6D7C3 SW10.1uFR2 20KOhmXTR116MHzC1 C233pF 33pFRSTX2X1U187C751P3.0P3.1P3.2P3.3P3.4P3.5P3.6P3.7LCM1Char LCD ModuleEVDDRSRWVLGND5V10KOhmR1Parts ListLCM1U1XTR1C1,C2SW1R1R2C3Part NumberHDM16216H-587C751NMP16033pF--10Kohm20Kohm0.1 uFDescriptionHantronix Alphanumeric LCD ModulePhillips Microcontroller16MHz CrystalCapacitorPush Button Switche (Reset)PotResistorCapacitor- Page 1 -

Application NoteINC.Crystal Clear and Visibly Superior LCD ModulesIII. Software Flowchart:BeginWriteP1 = 38h, Command_ByteData=[DPTR]4.1mSec DelayP1 = 38h, Command_Byte100uSec DelayInitialization?Data = 99hNoCall Data_ByteYesReturnP1 = 38h, Command_ByteP1 = 0ch, Command_ByteP1 = 01h, Command_ByteINC DPTRCGRAMFirst_LineSecond_Line:Command_byteData_byteIDLERS lowRS high*CGRAM: Program in CGRAM DATAFirst_Line: Display First LineSecond_Line: Display Second LineRW low - Enable writeDELAYE low - generate enable pulseStart TimerTestFlag = 0Timer0 Interrupt:TestFlag=1Stop TimernopTestFlag=1?NoYesReturnE high - pull up enable signalRW high - Read modeConfigure P1 to input portDB7 = 1?YesNoReturn- Page 2 -

Application NoteINC.Crystal Clear and Visibly Superior LCD Modules;**********************************************************;; Application Note:; =================; <strong>Displaying</strong> <strong>Characters</strong> on an LCD Character Module;; Description: Demo software to display “canned”message and custom characters..; Controller: Phillips 87C751; LCD controller: HD44780, KS0066, SED1278;;*************************************************************; Constant Definition;*************************************************************EnableT0 equ 082h ;enable timer0Disable equ 000h ;disable timerD4100h equ 00ch ;timer reload high byte def.D4100l equ 003h ;timer reload = 4.1mSec.D100h equ 000h ;timer reloadD100l equ 04ch ;timer reload = 100uSec.;*****************************************; Ram Definition;*****************************************Flags DATA 020h ;flagTstFlag BIT Flags.0 ;interrupt flag bit;*****************************************; Port Connections; =================; P1.0 -> D0; P1.1 -> D1; P1.2 -> D2; . . .; P1.7 -> D7; P3.0 -> Enable; P3.1 -> RS; P3.2 -> RW;*******************************************************; Interrupt Vectors; ------------------org 000hjmp PowerUp ; Power up reset vectororg 003hjmp ExInt0 ; External interrupt 0 vectororg 00bhjmp Timer0 ; Counter/ Timer 0 int vectororg 013hjmp ExInt1 ; External int 1 vectororg 01bh ;jmp Timer1 ; Timer 1 int vectororg 023hjmp I2C ; I2C serial int vectororg 50hPowerUp:;***** Timer 0 Interrrupt preparationclr TR ;disable timerclr TF ;clear overflow;**************************************; LCD Initialization Routine;**************************************cinit: clr P3.1 ;RS lowclr P3.2 ;RW lowsetb P3.0 ;Enablemov RTL,#D4100l ;set timer reload valuemov RTH,#D4100h ;dealy time = 4.1mSecsdone:mov p1,#38hacall command_byteacall ddelay ;initial delay 4.1mSecmov RTL,#D100l ;set timer reload valuemov RTH,#D100h ;dealy time = 100uSecmov p1,#38h ;function setacall command_byteacall ddelay ;busy flag not avail. yetmov p1,#38h ;function setacall command_bytemov p1,#0ch ;display onacall command_bytemov p1,#01h ;clear displayacall command_byteacall cgram ;define custom fontsacall first_line ;display first lineacall second_line ;display second linesetb IDLE ;power down modejmp sdone;********************************************************;Subroutine: WRITE;=================;Purpose: To feed in data/command bytes to the LCD module;Parameters:dptr = should be set to the beginning of; the data byte address; Data bytes should be finished with 99H;Alg: get a new data/command byte; while (new data != 99h) {; set port1 with new data; call data_byte; increment data pointer; }; return;********************************************************write:write_loop:mov a,#0movc a,@a+dptrcjne a,#99h,write_contretwrite_cont:mov p1,aacall data_byteinc dptrjmp write_loop;************************************************; Delay Routine:; Delay periond = 4/3uSec * DefRth,l;************************************************ddelay:setb TR ;start timermov IE,#EnableT0 ;enable timerclr TstFlag ;reset flagdloop: jnb TstFlag,dloopret;********************************; set address to beginning; of CG RAM;********************************- Page 3 -

Application NoteINC.Crystal Clear and Visibly Superior LCD Modulescgram:mov p1,#40hacall command_bytemov dptr,#cgram_dataacall writeret;********************************; Set DDRAM to the beginnig of; the first line - 00;********************************first_line:mov p1,#080h ;set DDRAMacall command_bytemov dptr,#fline_dataacall writeret;********************************; Set DDRAM to the beginning of; the second line - 40;********************************second_line:mov p1,#0c0h ;set DDRAMacall command_bytemov dptr,#sline_dataacall writeret;**********************************************************; Feed Command/Data to the LCD module;***********************************************************command_byte:clr p3.1 ; RS low for a command byte.jmp bdelaydata_byte:setb p3.1 ; RS high for a data byte.nopbdelay:clr p3.2 ; R/w low for a write modeclr p3.0nopsetb p3.0 ;enable pulsenop;******************* Check Busy Flagmov p1,#0ffh ;configure port1 to input modesetb p3.2 ;set RW to readclr p3.1 ;set RS to commandclr p3.0 ;generate enable pulsenopsetb p3.0bloop: nopmov a,p1anl a,#80h ;check bit#7 busy flagcjne a,#00h,bloop;keep waiting until busy flag clears;*****************************************; check busy flag twice;*****************************************bwait:mov a,p1anl a,#80hcjne a,#00h,bloopclr p3.2 ;return to write moderet;******************************************; Interrupt Routines;******************************************ExInt0:ExInt1:Timer1:I2C:reti;**********************************************Timer0:setb TstFlagclr TRmov IE,#Disablereti;********************************************; Data Bytes;*******************************************FLINE_DATA:db ‘>>> HANTRONIX