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--- pm:prj2025:iotelea:ana_maria.ailiesei [2025/05/27 23:58]
ana_maria.ailiesei [Software Design]
+++ pm:prj2025:iotelea:ana_maria.ailiesei [2025/05/28 00:35] (current)
ana_maria.ailiesei [Bibliography and Sources]
@@ Line 251: / Line 251: @@
     }
-== Documentation for I2C communication with the LCD ==
-This was the hardest part because I couldn't really find any code on any forum to help me with this. Here is the information i found in the datahseet [[https://cdn.sparkfun.com/assets/9/5/f/7/b/HD44780.pdf] | HD44780 Datasheet].
-In the Table 6 Instructions I found the addr4esses for the commands 0x01 (clear), 0x02 (home), 0x06 (entry-mode), 0x0C (display ON), 0x28 (function set 4-bit / 2-line). In figure 24 - 4 bit interface we can see how we have to initialise the lcd so that we can communicate in 4 bit mode. In the  Interfacing to the MPU section we see that the 4 bits of data must be sent twice, In figure 9 is explained how The nibble you put on DB7-DB4 is latched into the Instruction Register. The IR holds commands such as Function Set, Display On/Off, or an address for DDRAM/CGRAM. Data register (DR) read	1	1	You read the Data Register, which is a one-byte buffer in front of DDRAM/CGRAM. After the read, the controller automatically prefetches the next byte to DR.
 == GPIO ==
 Initializing the buttons:
@@ Line 285: / Line 276: @@
       joystickButtonPinInterrupt = true;
   }
+=== Documentation for the I2C communication with the LCD ===
+== Why those hex commands? ==
+x01 Clear Display, 0x02 Return Home, 0x06 Entry-Mode Set, 0x0C Display ON/OFF, 0x28 Function Set – their op-codes and bit-fields are listed in Table 6 "Instructions" of the datasheet.
+The Function Set constant 0x28 is 0010 1000b => DL = 0 (4-bit), N = 1 (2-line), F = 0 (5x8 font). You must send this after forcing the controller into 4-bit mode so it knows the final interface width.
+== Power-up initialisation (Figure 24 flow) ==
+<code>
+x30 -> 0x30 -> 0x30 -> 0x20
+</code>
+Send the "0x30 three times" handshake (still in 8-bit mode) and finally 0x20 to drop DL=0. This is the exact 4-bit initialisation sequence shown in Figure 24 "4-Bit Interface Initializing by Instruction" (under Initializing by Instruction).
+== 4-bit write cycle (Figure 9) ==
+In 4-bit mode each byte is split: high nibble first, low nibble second. Figure 9 labels the bus cycles:
+| RS | R/W | Cycle name | Purpose |
+| 0 | 0 | IR write | Latch a command or address into the Instruction Register |
+| 1 | 1 | DR read | Fetch data from DDRAM/CGRAM via Data Register |
+See Figure 9 "4-Bit Transfer Example" for the two Enable pulses per byte.
+== What the bit-flags in lcd_send_half() do ==
+| Bit mask | PCF8574 pin → LCD | Why it’s set |
+| 0xF0 | P4-P7 -> DB4-DB7 | Carry the nibble you’re transmitting |
+| 0x01 | P0 -> RS | 0 = command, 1 = data (selects IR or DR) |
+| 0x00 | P1 → R/W kept low | We only write; reads would need a separate read routine |
+| 0x04 | P2 -> E | Toggling E high->low latches the nibble; kept >450 ns with delayMicroseconds(2) |
+| 0x08 | P3 -> LED+ | Turns the backpack back-light on |
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 <html>
   <iframe width="560" height="315"
-     src="https://www.youtube.com/embed/rlgCxp-0uKw?si=nVdr1mpfgMVzz8b_"
+     src="https://www.youtube.com/embed/1_WvuHkVgRU"
      title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" referrerpolicy="strict-origin-when-cross-origin" allowfullscreen>
   </iframe>
@@ Line 347: / Line 370: @@
 [[https://www.flipkart.com/tumtafa-best-quality-labyrinth-game-ball-in-a-maze-round-wooden-kids-adults-party-fun-games-board/p/itm10a21ca18e84c?pid=BDGGGSTBHPG2E3WZ |Ball maze photo]]
+[[https://cdn.sparkfun.com/assets/9/5/f/7/b/HD44780.pdf | HD44780 Datasheet]]