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

[struppi81]

Hello Darrel,

yes your are right, very scary!

And yes I use the scope, because of controlling the puls length (µs).


What I have done again:

I reduce the code a little bit and I change/simplified some parts.

I replace this:

Char_Temp = Char << 1                                 ; Shift Up Lower 4 Bits  
Char_Temp = Char_Temp << 1
Char_Temp = Char_Temp << 1
Char_Temp = Char_Temp << 1 

with this:

Char_Temp = Char & %00001111                     ; Shift Up Lower4 Bits
@ swapf _Char_Temp ,F

Also I reduce the Upper an Lower Nibbel Part from 6 to only 4 Steps.

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, 3
    Char_Temp = Char_Temp | %00001000                    ; Set Enable Bit 
 Case 2
    Char_Temp = Char & %00001111                         ; Shift Up Lower4 Bits
    @ swapf _Char_Temp ,F
    If RSS = 1 Then : Char_Temp = Char_Temp | %00000100  ; Set RS Bit            
END SELECT

Because Toggle the Enable Bit again is not necessary.


Further, I change (Post 6, Point 2...."Although I have a feeling it can be reduced somehow")

This:

;----[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
Next  

To This:                                     

;----[Shift_Routine_74HC595 ]---------------(DO NOT Change)-------------------
ShiftLoop: 
For ShiftLoop_Steps = 0 to 6
 @ rlf _Bit_Shift, F                     ; Shift 1.Pos left
If STATUS.0 = 1 Then                     ; Carry Flag
   Serial_Pin = 0 : @  DelayUS 1         ; min 1 µs for 1
   Serial_Pin = 1 : @  DelayUS 15        ; min 15 µs
else
   Serial_Pin = 0 : @  DelayUS 15        ; min 15 µs for 0
   Serial_Pin = 1 : @  DelayUS 30        ; min 30 µs 
endif
next

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

Up to now, the code runs very good. (I Think a little bit better then before.)
But sometimes when I simulate it on the PC, after some time, the LCD shows only cryptic characters.
Then I have to restart the simulation again an all works fine.

What du you think, is there something one can improve?

Thanks in advance!

[Charlie]

Note also there will be a wide variation of timings across components, a wide variation of chip sensitivity, and a sensitivity to clock speed, temperature, power supply voltage, data rates, etc. etc. This approach is "O.K." for a hobby project, but it would be a very bad idea to try to use it in a commercial project, especially anything that might see volume.

Not to rain on your parade, but given you can get PIC devices with fewer pins and at lower cost than a 74HC595, you would be further ahead to create a dedicated display driver PIC that you can send data to by 1 pin serial. Fewer components too, and rock solid communications.