barcode scanner sdk vb.net Understanding a 16-CharaCter-by-2-Line LCd dispLay in Software

Encoder QR Code JIS X 0510 in Software Understanding a 16-CharaCter-by-2-Line LCd dispLay

Understanding a 16-CharaCter-by-2-Line LCd dispLay
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program 21-11
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Preliminary LCD Routines-Checking Program
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{{11 Oct 09 Harprit Sandhu LCDTester.Spin Propeller Tool Ver. 1.2.6 Test program for LCD Routines }} CON _CLKMODE=XTAL1+ PLL2X _XINFREQ = 5_000_000 high =1 low =0 VAR byte index OBJ LCD : "LCDRoutines" UTIL : "Utilities" PUB Go LCD.initialize_lcd LCD.print (string("Initialized OK")) LCD.position(2,1) LCD.print (string("Print test")) UTIL.pause (1500) LCD.clear LCD.position (1,1) LCD.print (string("this is 1st line")) UTIL.pause (300) LCD.position(2,1) LCD.print (string("ok is on line 2")) UTIL.pause (1500) LCD.clear LCD.print (string("Position test")) UTIL.pause (1500) index:=0 repeat 16 index := index +1 LCD.clear LCD.position (1,index) LCD.print (string("X")) UTIL.pause (300)
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program 21-11
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Preliminary LCD Routines-Checking Program (continued)
index:=0 repeat 16 index := index +1 LCD.clear LCD.position (2,index) LCD.print (string("X")) UTIL.pause (300) LCD.clear LCD.print (string("End")) Repeat
As you become more proficient in the use of Spin, you will want to make Program 21-11 more comprehensive and robust to check all the features you add to the LCDRoutines program. Program 21-11 is just the beginning. The Utilities program will contain the following two methods for now (we will add more methods as we need them):
FLASH Pulses a line (usually an LED) PAUSE Pause/delay program in milliseconds
The code for the Utilities program is given in Program 21-12.
program 21-12 Utilities
{{21 Sep 09 Harprit Sandhu Utilities0.spin Propeller Tool Ver 1.2.6 21 Program 12 Program UTILITIES Flash flashes a pin once, toggles it slowly Pause pause in milliseconds }} CON high low waitperiod
=1 =0 =100
PUB FLASH (color) outa[color] :=high waitCnt(waitPeriod +cnt) outa[color] :=low waitCnt(waitPeriod +cnt)
'routine to flash an LED by color 'line that actually sets the LED high 'wait till counter reaches this value 'line that actually sets the LED low 'wait till counter reaches this value ' PUB PAUSE(millisecs) 'As set up here it is .25 millisceconds waitcnt((clkfreq/1000)*millisecs +cnt) 'based on Osc freq
Understanding a 16-CharaCter-by-2-Line LCd dispLay
This completes what we need to have usable control of a 16-character-by-2-line LCD display in 8-bit mode. We will be using this 16 2 display for all our experiments, but we will use 4-bit mode so that we can free up four more lines on the Propeller. Four-bit mode is covered next.
4-Bit Mode
The use of the LCD in 4-bit mode has a few complications we need to understand. Because most data is expressed in 8 bits and only four data lines are connected to the LCD, some special procedures have to be followed to allow all 8 bits to be transferred to the LCD. In general, this is done by transferring the data in two steps, with 4 bits transferred in each step. When the LCD powers up, its condition is indeterminate. The first few instructions can be sent to it on four lines or on eight lines, but only bits 7 to 4 will be looked at by the LCD. The first three transmissions can be sent as %0011_0000 or as %0011. The fourth transmission has to be %0010 to set 4-bit mode. This is the last 4-bit transmission, because at the end of this transmission, the system is in 4-bit mode. In 8-bit mode, this would have been the high part of the %0011_1000 instruction (in 4-bit mode, this is %0010_1000 the 0 that replaces the 1 is the 4-bit mode specification). This means that the low nibble (%1000) has been ignored in the process. We pick this byte back up by transmitting the entire 8 bits (%0010_1000) again 4 bits at a time. The SEND_INSTRUCTION used in 8-bit mode is divided into two instructions in the LCDRoutines4 object:
SEND_INSTRUCTION sends just 4 bits. SEND_INSTRUCTION2 sends all 8 bits, 4 bits at a time.
All the routines in LCDRoutines that transmit 8 bits of data are modified to send 4 bits at a time for both characters and data. All these changes are incorporated into the LCDRoutines4 program listed in Program 21-13.
note Having accomplished this change to the LCD, in the future we will use 4-bit mode in all our experiments.
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