Serial LCD Problem, text prints slowly

[jayanth.devarayanadurga]

I have written a Serial LCD Code which uses 2 wires. The problem is the characters display one after the other and it is very slow. Why does the character print so slowly? I want it to display characters just like 4-bit non serial LCD prints i.e., I need it to print data fast so that it appears as if each line is printed as a whole.

I am attaching my project files and Proteus files.

 

[tpetar]

Remove waitUs.

Try modified code in attachment.


:wink:

 

[jayanth.devarayanadurga]

Thanks tpetar. It is much better now. I still modified the code. See below piece of code. I commented out the 2 delays in the for loop. I want to know is it ok to remove the delays in the for loop or is it necessary to have them? I tested it on Proteus after removing the 2 delays in the for loop and it is working perfectly.

I am attaching the new file.

---

Code C - [expand]
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for ( i=8;i>0;i=i>>1)
        {
                if(d & i)
                        {
                                data_ =1;
                        }
                        else
                        {
                                data_ =0;
                        }
                //waitUs(10);
                clk = 1;
                //waitUs(10);
                clk = 0;
        }

---

 

[tpetar]

It should be ok. Thats the problem with Proteus simulator you never know whether it will work or not on real hardware, that's why I always say nothing can replace developing board or protoboard with real hardware. Proteus is good as cheap variant if you dont have hardware, but it may be a waste of time.

Additional you can run uC on faster speed, try 16MHz, existing configuration is for 4MHz. :wink:

 

[jayanth.devarayanadurga]

Ok. I will try at 20 MHz and let you know.

 

[tpetar]

On 20MHz you get whole text almost instantly on LCD.

 

[jayanth.devarayanadurga]

Why it is slow when 4 MHz is used? All my C code is around 210 lines and if it is assumed that the assembly equivalent code will have around 2000 line code and each assembly instruction will take 6 clocks then total clock needed is 12000 clocks. 1 sec = 4000000 clocks, 12000 clocks = 3 ms. Even if it takes 3 ms then text should appear instantly.

 

[zuisti]

Why it is slow when 4 MHz is used?

Because your 'waitUs' function is bad (it is the same as the 'waitLcd') :

void waitUs(int x) {
   unsigned char i ;
   
   for (x ;x>1;x--) 
       for (i=0;i<=10;i++);
}

So the waitUs(10) is much more than 10 us: outer (x) loop runs 10 times, but the intern loop (i) itself longer than 40 us at 4 Mhz.
See the asm output...

 

[jayanth.devarayanadurga]

Thank you zuisti.

Can somebody explain this piece of asm code.

---

Code ASM - [expand]
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_waitUs:
 
;slcd.c,346 ::                 void waitUs(int x)
;slcd.c,349 ::                 for (x ;x>1;x--);
L_waitUs14:
        MOVLW      128
        MOVWF      R0+0
        MOVLW      128
        XORWF      FARG_waitUs_x+1, 0
        SUBWF      R0+0, 0
        BTFSS      STATUS+0, 2
        GOTO       L__waitUs32
        MOVF       FARG_waitUs_x+0, 0
        SUBLW      1
L__waitUs32:
        BTFSC      STATUS+0, 0
        GOTO       L_waitUs15
        MOVLW      1
        SUBWF      FARG_waitUs_x+0, 1
        BTFSS      STATUS+0, 0
        DECF       FARG_waitUs_x+1, 1
        GOTO       L_waitUs14
L_waitUs15:
;slcd.c,353 ::                 }
L_end_waitUs:
        RETURN
; end of _waitUs

---

 

[zuisti]

Can somebody explain this piece of asm code.

_waitUs:

;slcd.c,346 ::                 void waitUs(int x)  //[COLOR="#FF0000"]unfortunately (and unnecessarily)
                                                    // the parameter x is a signed int !![/COLOR]

;slcd.c,349 ::                 for (x ;x>1;x--);   //[COLOR="#FF0000"]line 349 in the C source[/COLOR]
L_waitUs14:
        MOVLW      128
        MOVWF      R0+0
        MOVLW      128
        XORWF      FARG_waitUs_x+1, 0 //[COLOR="#FF0000"]the signed 'x > 1' examining is such complicated :-([/COLOR]
        SUBWF      R0+0, 0
        BTFSS      STATUS+0, 2
        GOTO       L__waitUs32
        MOVF       FARG_waitUs_x+0, 0  //[COLOR="#FF0000"]the 'FARG_waitUs_x+0 (and  +1) is the parameter x (2 bytes) [/COLOR]
        SUBLW      1
L__waitUs32:
        BTFSC      STATUS+0, 0           //[COLOR="#FF0000"]if carry then end else continue[/COLOR]
        GOTO       L_waitUs15
        MOVLW      1
        SUBWF      FARG_waitUs_x+0, 1   //[COLOR="#FF0000"]the 'x--' is also such complicated :-([/COLOR]
        BTFSS      STATUS+0, 0
        DECF       FARG_waitUs_x+1, 1
        GOTO       L_waitUs14
L_waitUs15:
;slcd.c,353 ::                 }
L_end_waitUs:
        RETURN
; end of _waitUs

So use here an (unsigned) char parameter!

 

[jayanth.devarayanadurga]

Should I use Delay_us(20) instead?

 

[zuisti]

Should I use Delay_us(20) instead?

Yes, but the Delay_us(1) is also enough . Try it!

 

[jayanth.devarayanadurga]

Ok. Thanks zuisti.

I tried but if I use 10us delay it works upto MCU clock 16 MHz. For 20 MHz LCD display is blank. If I use 20us delay then it works at 20 MHz also.

 

[jayanth.devarayanadurga]

Serial LCD working at 20 MHz.