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

[struppi81]

Thanks Darrel,

now I'm wiser, again thanks.

With the delays......

To shift out one byte (Data or Command) after LCDInit it needs 4 Steps.
One Step require a time nearly 910µs - 1ms.
That makes nearly 4ms. => No extra Delay necessary. Right?

The First 4 commands in the LCD_Init part needs only 2 Steps, because only the 4 upper bits shifted out.
There, I'm agree with you that the delay should be longer.

Could I place them here: ?

LCD_Init:
    ShiftOut_Steps = 1
    Char = $33 : gosub  LCDsendCOM : @  DelayUS 5000
                 gosub  LCDsendCOM : @  DelayUS 600
                 gosub  LCDsendCOM : @  DelayUS 600                
    Char = $22 : gosub  LCDsendCOM : @  DelayUS 600  ; Start 4-bit mode
    .........
    .........
    .........

Further I tested again with other frequencies.
I use 8 Mhz and a 20 Mhz quarz.
Also there are, no problems. It runs stable.

What I find out is that it is absolute necessary, to add an capacitor between +V and GND of the 74HC595.
I use an 100nF.
Otherwise you get sometimes error in displaying the right things.

The capacitor for the Latch Pulse, I would change back to 2.2nF. And the capacitor for the 1 or 0 Pulse should be left at 4.7nF.

Here are some picture make with my mini DSO.

Clock Pulse


Pulse 1 or 0 with 2.2nF


Pulse 1 or 0 with 4.7nF


Latch 2.2nF & Latch 4.7nF

[Darrel Taylor]

To shift out one byte (Data or Command) after LCDInit it needs 4 Steps.
One Step require a time nearly 910µs - 1ms.
That makes nearly 4ms. => No extra Delay necessary. Right?

No, each byte whether it's a command or data requires two nibbles at 910 uS or 1.82 mS total.

You need the delays!

And I would leave the initialization timing the same.
It only happens once per power-on, so you're not saving any time during normal operations.