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Hi all.. Im quite new to 8051. Im doing a project that requires me to display value of a peak voltage on a LCD.
Anyway, Im stuck in testing the LCD. I have connected the LCD(Powertip PC 0802-A), otherwise known as 214-3288, to my 8051 development kit. The kit that im using is C8051F206-TB. I connected databus 0-7 to port 3 and RS to P2.4, R/W to P2.5, and EN to P2.6
I also have gone online to source for programs to display "Hello World" on the LCD. I have found a few in C or asm, but i have learnt the basic of assembly language, so i don't really understand C language.
Below is a program i found in 8052.com
$include (c8051f200.inc) CSEG AT 0000H LJMP MAIN CSEG AT 0100H MAIN:LCALL CONFIG LCALL INIT_LCD LCALL CLEAR_LCD LCALL HELLO CONFIG:MOV PRT0MX, #000H ; PRT0MX: Initial Reset Value MOV PRT1MX, #000H ; PRT1MX: Initial Reset Value MOV PRT2MX, #000H ; PRT2MX: Initial Reset Value MOV P2MODE, #0FFH ; Input Configuration for P2 MOV PRT3CF, #0FFH ; Output configuration for P3 INIT_LCD: CLR P2.4 MOV P3,#38H SETB P2.6 CLR P2.6 LCALL WAIT_LCD CLR P2.4 MOV P3,#0EH SETB P2.6 CLR P2.6 LCALL WAIT_LCD CLR P2.4 MOV P3,#06H SETB P2.6 CLR P2.6 LCALL WAIT_LCD RET HELLO: LCALL INIT_LCD LCALL CLEAR_LCD MOV A,#48H LCALL WRITE_TEXT MOV A,#45H LCALL WRITE_TEXT MOV A,#4CH LCALL WRITE_TEXT MOV A,#4CH LCALL WRITE_TEXT MOV A,#4FH LCALL WRITE_TEXT CLR P2.4 MOV P3,#0CAH SETB P2.6 CLR P2.6 LCALL WRITE_TEXT MOV A,#57H LCALL WRITE_TEXT MOV A,#4FH LCALL WRITE_TEXT MOV A,#52H LCALL WRITE_TEXT MOV A,#4CH LCALL WRITE_TEXT MOV A,#44H LCALL WRITE_TEXT WAIT_LCD: CLR P2.6 ;Start LCD command CLR P2.4 ;It's a command SETB P2.5 ;It's a read command MOV P3,#0FFH ;Set all pins to FF initially SETB P2.6 ;Clock out command to LCD MOV A,P3 ;Read the return value JB ACC.7,WAIT_LCD CLR P2.6 ;Finish the command CLR P2.5 ;Turn off RW for future commands RET CLEAR_LCD:CLR P2.4 MOV P3,#01H SETB P2.6 CLR P2.6 LCALL WAIT_LCD RET WRITE_TEXT:SETB P2.4 MOV P3,A SETB P2.6 CLR P2.6 LCALL WAIT_LCD RET END
So i have to check the signals by using either an oscilloscope or a logic analyzer in order to make make sure that it is about the same diagram as the write diagram? So where do i get the signals from? From the LCD or the development kit?
Also, how can i check whether my circuit satisfy the rise time to use the display?
Yes, that is the ideal way to do it. You certainly couldn't check EN rise/fall times without a scope, or the power supply rise time for that matter. I think a lesser that ideal way to do it was commented on above; calculating the time to execute the instructions that control various signals. A simple calculation would tell you if you are close to not satisfying timing. I mean if EN must be high for at least 450ns and you're running a 40MHz 1-clocker, back-to-back SET/CLR instructions are going to be way shorter than 450ns.
As for the power supply rise time being fast enough to qualify for relying on the internal reset circuit, one could simply avoid the issue entirely and execute the "initialization by instruction" even if it wasn't necessary. It's merely a slower, safer way to initialize the display.
Oh.. I see. But where do i get signals from? Isit for EN, I have to probe the signal only from the EN pin on the LCD and the same for RS and RW?
Well signals have two ends, right? And sometimes intermediate access points in between. It is usually best to measure the signals at the device whose timing requirements you are trying to satisfy, so in your case, probably near the display connector.
So i have to probe one end to the pin that i want to see the signal and the other end to gnd?
Right.
I see. Thanks alot for your help guys!!! If i run into some other problems, i'll post again =P For now, Im going to enjoy my weekend!!!
Regards natur3
Erm.. Guys.. I probed the pin as you told me, but i get no waveform. Do i have to power up the 8051 board when measuring the LCD's EN rise/fall time. Also how do i write the "initialization by instruction"? I have seen the diagram but i do not understand. This is where i downloaded the initialization file.
docs-asia.electrocomponents.com/.../0900766b800b9873.pdf
I forgot to give the link for the instruction set. It is as follow:
docs-asia.electrocomponents.com/.../0900766b800b9869.pdf
The waveform will only come when i send a signal to the LCD?
And for the "initialization by instruction", do i have to put a delay routine for those "waiting 15ms,4.1ms,etc"?
Theres also 3 instructions of function set. Do i have to run the instruction 3 times?
Lastly, after the 3rd sequence, is there no delay between "display off", "display clear" and "entry mode set"?
"...i get no waveform. Do i have to power up the 8051 board when measuring the LCD's EN rise/fall time?"
Errr... rather definitely yes!!
EN is an input to the LCD, so it must be generated by the 8051 - obviously, the 8051 will not be generating anything at all if it isn't powered-up!!
You need to go back to basics to understand how the LCD actually works - see: www.8052.com/tutlcd.phtml and: www.8052.com/tutlcd2.phtml
One important note. You should not power up the LCD without powering up the 8051. And in reverse, you should not power up the 8051 without powering up the LCD.
Most integrated circuits does not support voltages received on any signal pins, without already having the supply voltage turned on.
If you look at data sheets, there is normally a note how many volt a signal pin may be forced above VCC (or below GND). This value is normally somewhere between 0.2V and 0.7V.
If the signal pin is held outside this value, you may get latchup problems (the pin locks at the forced value for minutes or hours) or you may permanently kill the signal or the whole chip! Note that the chip can also gradually deteriorate, i.e. it can seem that it survives the abuse for a couple of times, before the signal or chip permanently fails!
Always make sure that all VCC pins of all chips in a circuit always gets their power at the same time. If a circuit is using more than one voltage, there is often need for diodes between the different supplies, to make sure that the fastest rising supply voltage helps a slower supply to rise.
When interfacing electronics with external signals (where you don't have control over when signals are applied with relation to availability of supply voltages) you normally need special buffer chips - or high-impedive serial resistors with optional protection diodes from the signal to VCC and GND.
If you are working with a prototype and are not 100% sure if your program is correct - or if your prototype is correctly wired - it is extra important to make sure that you doesn't also have to worry about some signal pins being broken on a chip...
You mean i have to power up my board and LCD at the same time?
"If a circuit is using more than one voltage, there is often need for diodes between the different supplies"
Does the above sentence mean that i have to add a diode to the circuit? Because the board and the LCD uses different supply. If needed, how do i connect?
I have read and understand most part of the tutorial.
What happens when the EN's timing does not satisfy the spcified timing requirements? What do i have to do?
Also, what does NOP mean? The tutorial said if my crystal is too fast, i have to create an number of NOP delay so that it meet the datasheet timing.
I have also probe when sending a signal to the LCD. I saw a sawtooth waveform. It does not show the waveform on the datasheet.
"What happens when the EN's timing does not satisfy the spcified timing requirements?"
The behaviour is undefined.
"What do i have to do?"
You have to comply with the specifications specified in the Datasheet
"Also, what does NOP mean?"
NOP is the 8051 "No-Operation" instruction.
The full set of 8051 instructions is described in Chapter 2 of the so-called "bible" for the 8051:
Chapter 1 - 80C51 Family Architecture: www.nxp.com/.../80C51_FAM_ARCH_1.pdf
Chapter 2 - 80C51 Family Programmer's Guide and Instruction Set: www.nxp.com/.../80C51_FAM_PROG_GUIDE_1.pdf
Chapter 3 - 80C51 Family Hardware Description: www.nxp.com/.../80C51_FAM_HARDWARE_1.pdf
Sounds like you also need to read the basic Tutorial on the 8051:
www.8052.com/tut8051.phtml
And maybe get yourself a good book: http://www.keil.com/books/8051books.asp www.8052.com/books.phtml
ok... In order to use NOP, i will have to check my crystal and calculate the number of NOPs to be inserted into the program? I have a problem here. My board only have internal oscillator which have a freq of 2-16Mhz.
Although i managed to make the cursor blink sometimes, but whenever i run the program, the LCD seems to go into chaos mode. I can see lines moving very fast.
Also, when i stop the program, theres an error which says:
"Target did not halt! Some circumstances cause a slow hardware response. Do you want to retry?"
and when i click "ok", it goes back to before i download the program into the LCD.
but when i click "Cancel", another pop-up says: "Target failed to respond. System is being disconnected"
What does this error means?