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

[struppi81]

Here I'm again.

Again to my last post:
I think over it again and C Flag is also an System Variable.
Also too unsuitable.

What have I done:

I rewrite the code once again.
I change the Variable Name's an insert your code from Statement 2.
Could it be, that there is an small mistake.

F  var byte
G  var byte

;D = B >> E
F = E
G = B
ShiftLoop
   ;G = G >> 1
    G = G << 1
    F = F - 1
IF F != 0 THEN ShiftLoop
;D = G.0
D = G.7

Once Again here is the code

Char_Temp             var byte
ShiftOut_Steps        var byte
Count_ShiftOut_Steps  var byte
ShiftLoop_Steps       Var byte
Bit_Shift             Var byte
Readout_Bit           var bit

INCLUDE "VirtualPort.bas"

LCD_DATAUS    CON 2000
LCD_COMMANDUS CON 50

Goto Over_One_Wire_74HC595

;===============( DO NOT Change anything below this line )====================

ASM ; Make sure HighJack has been installed in PBP's .LIB file
    ifndef LCDOUT_HIGHJACKED 
        error "HighJacked-LCDOUT Not found in PBPPIC??.LIB"
    endif
ENDASM
DEFINE  HJ_LCDOUT  _LCDsend    ; Redirect PBP's LCDOUT to LCDsend: Subroutine

;----[Send a byte to the Virtual LCD PORT]------------(DO NOT Change)---------
TempChar        var  byte
Char            VAR  Byte
LCD_Initialized VAR  FLAGS.1
RSS             VAR  FLAGS.0                ; LCD RS State

;----[ This routine is called once for every character sent by LCDOUT ]-------
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 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:
return

;----[Initialize the LCD]-------------------(DO NOT Change)-------------------
LCD_Init:
    ShiftOut_Steps = 2
    Char = $33 : gosub  LCDsendCOM : @  DelayUS 5000
                 gosub  LCDsendCOM : @  DelayUS 100
                 gosub  LCDsendCOM : @  DelayUS 100                 
    Char = $22 : gosub  LCDsendCOM   ; Start 4-bit mode
    
    ShiftOut_Steps = 5
    Char = $28 : gosub  LCDsendCOM   ; Function Set, 4-bit, 2-line, 5x7
    Char = $0C : gosub  LCDsendCOM   ; Display ON
    
    Char = $06 : gosub  LCDsendCOM   ; Entry Mode
    LCD_Initialized = 1              ; LCD has been Initialized
goto LCDAfterInit

;----[Send it to 74HC595]-------------------(DO NOT Change)-------------------

ShiftLoop_Char:
For Count_ShiftOut_Steps = 0 to ShiftOut_Steps           ' For To Loop
SELECT CASE Count_ShiftOut_Steps
 CASE 0
    Char_Temp = Char & %11110000                         ; Isolate Upper 4 Bits 
    If RSS = 1 Then : Char_Temp = Char_Temp | %00000100  ; Set RS Bit          
 CASE 1, 4
    Char_Temp = Char_Temp | %00001000                    ; Set Enable Bit 
 CASE 2, 5 
    Char_Temp = Char_Temp ^ %00001000                    ; Toggel Enable 
 Case 3     
    Char_Temp = Char << 1                                ; Shift Up Lower 4 Bits  
    Char_Temp = Char_Temp << 1
    Char_Temp = Char_Temp << 1
    Char_Temp = Char_Temp << 1 
    If RSS = 1 Then : Char_Temp = Char_Temp | %00000100  ; Set RS Bit            
END SELECT
Bit_Shift = Char_Temp

;----[Shift_Routine_74HC595 ]---------------(DO NOT Change)-------------------
ShiftLoop_Steps = 7

ShiftLoop: 

Readout_Bit = Bit_Shift.7
SELECT CASE Readout_Bit
CASE 1 
  Serial_Pin = 0 : @  DelayUS 1         ; min 1 µs for 1
  Serial_Pin = 1 : @  DelayUS 15        ; min 15 µs 
Case 0
  Serial_Pin = 0 : @  DelayUS 15        ; min 15 µs for 0
  Serial_Pin = 1 : @  DelayUS 30        ; min 30 µs 
END SELECT

Bit_Shift = Bit_Shift << 1
ShiftLoop_Steps = ShiftLoop_Steps - 1
IF ShiftLoop_Steps != 0 THEN : Goto ShiftLoop

;Latch
Serial_Pin = 0 : @  DelayUS 200        ; min 200 µs for Latch 
Serial_Pin = 1 : @  DelayUS 300        ; min 300 µs

'Count_ShiftOut_Steps = Count_ShiftOut_Steps + 1                       ' for If Then Request
'IF Count_ShiftOut_Steps != ShiftOut_Steps Then : goto ShiftLoop_Char  ' for If Then Request
Next                                                                   ' For To Loop
Goto After_ShiftLoop_Char

Over_One_Wire_74HC595:

I also wanted to replace the For To Loop with an normal If - Then request, because of the Usage of System Variables; or is there neither.
It also works well but when I simulate it, it takes too much CPU Usage and Runs very slow.
Using an Repeat Until Loop also.
With an For To Loop the simulation is better.

But which Loop is the best, when one think only about the Usage in an Microcontroller?
What did you say. Is it OK or is there something which one can also improve.

Thanks in advance!

[Darrel Taylor]

STATUS,C is not a PBP system variable. You can use it.

FOR loops, REPEAT/UNTIL, WHILE/WHEN, DO/LOOP all do not use the system vars (as long as the test condition is = or !=).
They will use system vars if the test condition is <, <=, >, >= etc.

Speed differences between any of the loop types will not be significant on a real chip.
The major slow down with this interface is the timing required to activate inputs on the 595 using the capacitors.
All those delays in the code make writing to the LCD very slow.

[Darrel Taylor]

Your include looks better with the new variable names.
I ran it this morning, and it seems to be working.

Have you looked at the signals going to the 595 on a scope?
Scary stuff to be putting in a digital chip.

Yellow is the serial data.
Blue is after the 1.5K resistor.
Magenta is after the 33K resistor.



And you can see that it takes 910 uS per nibble (1.82 mS per byte).

It would be interesting to see how it works on real hardware.