Driving a 2x16 LCD with only One Pin and 74HC595

[struppi81]

Hello,

Yesterday I tested it with an 12F675 at 4 Mhz intOSC and till now it runs stable and fast.
When I less busy, I will test it out with other frequencies.

But i have yet again an comprehension question to this code:

LCDsend:
      @  MOVE?AB  _TempChar                 ; Get char sent by LCDOUT, in WREG
      if !LCD_Initialized then LCD_Init     ; Make sure LCD was Initialized 
  LCDAfterInit:
      if TempChar = $FE then RSS=0 : goto LCDsendDone   goto DONE ; next char is Command 
      Char = TempChar
  LCDsendCOM:  
      Goto ShiftLoop_Char
  After_ShiftLoop_Char:
      IF RSS = 0 then                       ; Is a Command
          IF Char = 1 then CommandDelay     ; Long delay for Clear Screen
          IF Char = 2 then CommandDelay     ; Long delay for Home
          @  DelayUS   _LCD_DATAUS          ; Short delay for everything else
          goto DelayDone
      else                        
          @  DelayUS   _LCD_DATAUS          ; Short delay for Data
          goto DelayDone
      endif
  CommandDelay:
      @  DelayUS   _LCD_COMMANDUS
  DelayDone:
    if LCD_Initialized then RSS = 1       ; Set RS to Data next time
  LCDsendDone:
  bsf     STATUS, C       ; Set no timeout for Serout2mod  
return

When i compare these steps with them in pbppic14.lib, than i note that in the upper code some parts (Red marked) not exist, like in the library code.

@ Darrel:
Are these Commands not necessary or why didn't you include them?


Further I would shrink this code to this:

LCDsend:
      @  MOVE?AB  _TempChar                 ; Get char sent by LCDOUT, in WREG
      if !LCD_Initialized then LCD_Init     ; Make sure LCD was Initialized 
  LCDAfterInit:
      if TempChar = $FE then RSS=0 : goto LCDsendDone ; next char is Command 
      Char = TempChar
  LCDsendCOM:  
      Goto ShiftLoop_Char
  After_ShiftLoop_Char:     
    if LCD_Initialized then RSS = 1       ; Set RS to Data next time
  LCDsendDone: 
return

Because of the fact, that the shifting time of 1 byte needs about 2 - 4ms, it is not nessesary to include extra Delays for Data or Commands.

Can I do it in this way?



Thanks in advance!

[Darrel Taylor]

If you use GOTO DONE, it limits the use of your include to 14-bit devices.
In the 18F library, it's called DUNN.

There's no need to use DONE, since the FSR hasn't been changed, and RETURN resets the BANK to 0 anyhow.

The bsf STATUS, C is only required if the end user is using the SEROUT2 command with a Flow Control Pin.
My observations have concluded that nobody uses that function. Or if they understand how to use Flow Control, they probably aren't using LCD_AnyPin.

However, to cover ALL the bases ... you are correct! bsf STATUS, C should be there. But it needs an @ sign.

As for removing the delays ... I don't think that's a good idea.
The measurement I took previously was 1.8 mS per byte.
Most good LCD's take 1.6 mS for a Clear Screen, so it would be fine (with a good LCD).
But there are LCD's that take longer, 2.4 mS is not uncommon.

You could remove the LCD_DATAUS part since it will always be under 1.8 mS.

But I think the ability to add delays for LCD_COMMANDUS should remain in the program.
You can easily set LCD_COMMANDUS to 0 in the main program for normal displays.
For slower LCD's, just set it to the difference of say 2.4 mS - 1.8 ms = 0.6 mS or 600 uS.