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?
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"?
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