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
Erm.. i forgot to say what help i needed... lol...
Can anyone help me to check where the program is wrong or whether i have connected the pins wrong.
By the way, the input voltage of the LCD is connected to a 5V supply and the contrast pin is connected to a 10k variable resistor. I have tried using stepping to find out the problem. I found out that the program keep looping here after the 1st LCALL WAIT_LCD
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
Does EN's timing satisfy the specified timing requirements?
Sorry, but i don't really get what you mean. Isit the En cycle time or the En rise/fall time u are talking about? Sorry.. Im really new to LCD programming...
Dan Henry asked, "Does EN's timing satisfy the specified timing requirements?"
natur3 t0mAt0 replied, "...Is it the En cycle time or the En rise/fall time"
They both form part of "the specified timing requirements"!
Oh. i see. sorry to bother u guys again. but what is the specified timing requirements? How do i check?
"what is the specified timing requirements? How do i check?"
That will be in tha Datasheet for the LCD.
ok.. I found the timing characteristics. Is it all this?
Enable cycle time Enable pulse width ("High" level) Enable rise/fall time Set-up time (RS,R/W,E) Address hold time Data Set-up time Data delay time Data hold time (writing) Data hold time (reading) Clock oscillating frequency
But how do i read these numbers? The datasheet gave me the symbols, min,max and the unit which is in nanosec. I don't know what these means...
If you don't have an oscilloscope to actually measure the signals, you will have to measure, evaluate or guestimate the number of clock cycles the processor needs when performing different operations. You will then have to make sure that all signal changes are made in the correct sequence and with enough delay.
I haven't looked at this specific data sheet, but the numeric parameters in the data sheet should be displayed somewhere in a timing diagram, where you can see between which points in the timing diagram that a specific parameter measures. Then you must make sure that you are always within the min and/or max times for that parameter.
For example: When writing data to the display, you must first emit the data before latching the data. The data sheet will specify the minimum ns the data must be stable before the strobe signal is toggled to latch the data. It will also show how many ns the data must continue to be stable after the latch/strobe signal is toggled again.
"data setup time" is normally how long before, you must have the data stable. "data hold time" is normally how long you must continue to hold the data stable after the latch operation. "data delay time" is how long time it takes for the display to drive the data signals to correct value when you issue a read command.
However, the data sheet should contain clear timing diagrams for these, and then it should be quite easy to understand what the parameters to, and why they are important.
Erm.. I think i get what u mean for the clock cycles. You meant i have to calculate the clock cycles for each routine and make sure that they have enuff delay? Does that mean i have to make another routine called "Delay" and call it from the other routine?
"correct sequence": The routines have to be in a correct sequence? I thought they can be called from anywhere in the program?
Also i do not know what you meant by the data have to be stable before latching and so on.
The datasheet have 2 charts; 1 for write and 1 for read. But i do not understand. if possible, it'll be great if there is a example code to tell me exactly what the timing means.
Thanks in advance.
You do not need any delay function. The required delays are very, very short. Most often, the required delays are shorter than the max speed the CPU can toggle signals. However, you have to make sure.
The timing sequences shows in which order different signals should be toggled to make sure that all required signals have correct values when they are needed.
If I show you a paper, and then remove it again and ask you to read it, you would not be able to. When you tell the display to read a value (when you write to the display), that value must already be available for the display to read. The value you write to the display (requests the display to read) must continue to be available until a while after you stop telling the display to read it.
All such requirements are graphically displayed in the data sheet, as timing or sequence diagrams. They show when a specific signal may take any value, when it must be low and when it must be high.
Well, in my datasheet, there is 2 diagrams, one for write operation and one for read operation. But i do not understand these diagrams. You might want to go this website: docs-asia.electrocomponents.com/.../0900766b800b986e.pdf
as this is where i Downloaded timing datasheet.
You meant i have to calculate the clock cycles for each routine and make sure that they have enuff delay?
Not quite. You will have to determine the timing of those signals. Calculating is only one of many ways of determining it, and hardly ever the best one to choose.
The best method would be to use an oscilloscope or logic analyzer on the actual hardware. If you really can't get your hands on a 'scope, the next best thing is the logic analyzer built into the uVision simulator debugger. Using that, you can generate almost exactly the same kind of diagram as you'll find in the datasheet(s) of devices you're trying to control. That can make things a whole lot easier to check.
"in my datasheet, there is 2 diagrams, one for write operation and one for read operation. But i do not understand these diagrams"
The Write diagram is showing:
1. The first thing that must happen is that R/W must either already be low, or be taken low, and RS must have reached its steady state for the operation
2. A time tAS must then elapse before E reaches its high-level threshold, VIH1
3. The time that it takes E to rise from its low-level threshold, VIL1, to VIH1 is called its rise-time and is specified by tEr
4. E must remain high for a time tDSW after the Data lines DB0~DB7 stabilise to valid levels
5. The Data line must remain valid for a time tH after E falls below VIL1
etc
Looking closer at your code, it appears that the display uses the ubiquitous Hitachi HD44780 controller or similar. It also appears that the code is designed to pace display writes by checking the controller's busy flag and it does so after writing the very first display instruction. Relying on proper busy flag operation right from the start like that require using the display with internal reset. When using the internal reset, the electrical characteristics in the controller data sheet's "Power Supply Conditions Using Internal Reset Circuit" table must be satisfied; otherwise, an "initialization by instruction" sequence must be used. It isn't until after the third step in the "initialization by instruction" sequence that the busy flag can be used reliably.
So, there is another aspect of timing for you to check before using that code you found on the Internet, and that is the power supply rise time. Does your circuit satisfy the rise time requirements to use the display without employing the "initialization by instruction" sequence?
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?
I have a problem here. My board only have internal oscillator which have a freq of 2-16Mhz.
Why is this a problem?
It doesn't matter what kind of oscillator you are using, it's how fast you run the processor that matters. The only thing to note is that if you run a processor with a RC oscillator, the frequency error of the oscillator may be very high, so the safety margins must be correspondingly higher.
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