Using the 12864-06D display, and how does flipmode work?

[RvanDeelen]

So a while ago i bought some displays of aliexpress. As one does. They were explicitly specified as being "right to left written".
It took me ages to get t the right constructor but in the end i found out that "U8G2_ST7565_NHD_C12864_1_4W_SW_SPI" will work. Because before this i used U8G2_ST7565_KS0713_1_4W_SW_SPI constructor, but altered the ADC reversal line manually in the library.
So now everything is oriented correctly (writing left to right and no mirrored letters), For my use case i did have to use rotation R2 but that's besides the point.

Something i don't understand tho is how the flipmode works in the constructor code. how can i know if the flipmode instruction actually works looking at the library?

[olikraus]

The code for flipmode is only sent to the display if the flipmode command (https://github.com/olikraus/u8g2/wiki/u8g2reference#setflipmode) is used. Ideally setFlipMode(0) should be executed automatically by the constructor. Unfortunately this isn't done (I missed this very early in the development now I am too lazy to fix this).
As a result, the commands for flip mode 0 must be implemented in the constructor startup code and in the flipmode 0 sequence itself.

In your case:

u8g2/csrc/u8x8_d_st7565.c

Line 804 in d9402d5

uint8_t u8x8_d_st7565_ks0713(u8x8_t *u8x8, uint8_t msg, uint8_t arg_int, void *arg_ptr)

The flip mode sequence is sent here:

u8g2/csrc/u8x8_d_st7565.c

Lines 819 to 830 in d9402d5

	case U8X8_MSG_DISPLAY_SET_FLIP_MODE:
	if ( arg_int == 0 )
	{
	u8x8_cad_SendSequence(u8x8, u8x8_d_st7565_flip1_seq);
	u8x8->x_offset = u8x8->display_info->default_x_offset;
	}
	else
	{
	u8x8_cad_SendSequence(u8x8, u8x8_d_st7565_flip0_seq);
	u8x8->x_offset = u8x8->display_info->flipmode_x_offset;
	}
	break;

And the commands are repeated in the normal startup sequence of that display:

u8g2/csrc/u8x8_d_st7565.c

Lines 787 to 802 in d9402d5

	static const uint8_t u8x8_d_st7565_ks0713_init_seq[] = {
	U8X8_START_TRANSFER(), /* enable chip, delay is part of the transfer start */
	U8X8_C(0x0ae), /* display off */
	U8X8_C(0x0e2), /* soft reset */
	U8X8_C(0x0a3), /* LCD bias 1/9 */
	U8X8_C(0x0a0), /* ADC set to reverse */
	U8X8_C(0x0c0), /* common output mode */
	U8X8_C(0x02f), /* all power control circuits on (regulator, booster and follower) */
	U8X8_C(0x026), /* set V0 voltage resistor ratio to max */
	U8X8_C(0x0a6), /* display normal, bit val 0: LCD pixel off. */
	U8X8_CA(0x081, 0x010), /* set contrast, contrast value, EA default: 0x016 */
	U8X8_C(0x0af), /* display on */
	U8X8_END_TRANSFER(), /* disable chip */
	U8X8_END() /* end of sequence */
	};

Which is actually defined here:

u8g2/csrc/u8x8_d_st7565.c

Lines 59 to 73 in d9402d5

	static const uint8_t u8x8_d_st7565_flip0_seq[] = {
	U8X8_START_TRANSFER(), /* enable chip, delay is part of the transfer start */
	U8X8_C(0x0a1), /* segment remap a0/a1*/
	U8X8_C(0x0c0), /* c0: scan dir normal, c8: reverse */
	U8X8_END_TRANSFER(), /* disable chip */
	U8X8_END() /* end of sequence */
	};
	static const uint8_t u8x8_d_st7565_flip1_seq[] = {
	U8X8_START_TRANSFER(), /* enable chip, delay is part of the transfer start */
	U8X8_C(0x0a0), /* segment remap a0/a1*/
	U8X8_C(0x0c8), /* c0: scan dir normal, c8: reverse */
	U8X8_END_TRANSFER(), /* disable chip */
	U8X8_END() /* end of sequence */
	};

But it seems, that the flip mode sequences are wrong. and the code for flip mode 0 and startup do not match.
In startup we have the commands 0xa0 and 0xc0, however flipmode 0 will send the wrong code 0xa1 0xc0.
This means, the display will be ok as long as you do not use the flipmode command, but will destroy the content after first use of flipmode.

Is this the problem you observed?

To fix this, I need to change

u8g2/csrc/u8x8_d_st7565.c

Line 822 in d9402d5

u8x8_cad_SendSequence(u8x8, u8x8_d_st7565_flip1_seq);

to zflip1 and

u8g2/csrc/u8x8_d_st7565.c

Line 827 in d9402d5

u8x8_cad_SendSequence(u8x8, u8x8_d_st7565_flip0_seq);

to zflip0

hmm looks like a bug in u8g2...

[olikraus]

Created issue #1792 for this.
Lets continue the discussion there.