## 06 LCD

The special function register `LCD`  memory mapped to addresses 4104 and 4105 enables HACK to write bytes to the LCD controller chip ILI9341V situated on MOD-LCD2.8RTP. The communication protocol is SPI with one additional wire DCX. The protocol defines transmission of 8 bit commands with DCX = 0 followed data with DCX=1. Data packets can have any length depending on the launched command.

### Chip specification

| IN/OUT | wire    | function                                           |
| ------ | ------- | -------------------------------------------------- |
| IN     | in[7:0] | byte to be sent.                                   |
| IN     | in[8]   | =0 send byte and set CSX low                       |
| IN     | in[8]   | =1 pull CSX high without sending byte              |
| IN     | in[9]   | value of DCX when transmitting a byte.             |
| IN     | load    | initiates the transmission of a byte, when in[8]=0 |
| IN     | load16  | initiates the transmission of 16 bit in[15:0]      |
| OUT    | out[15] | =0 chip is busy, =0 ready                          |
| OUT    | DCX     | =0 command, =1 data                                |
| OUT    | SDO     | serial data out                                    |
| OUT    | SCK     | serial clock                                       |
| OUT    | CSX     | chip select not                                    |

The special function register `LCD` communicates with ILI9341V LCD controller over 4 wire SPI.

When load=1 and in[8]=0 transmission of byte in[7:0] is initiated. CSX is goes low (and stays low even when transmission is completed). DCX is set to in[9]. The byte in[7:0] is send to SDO bitwise together with 8 clock signals on SCK. During transmission out[15] is 1. After 16 clock cycles transmission is completed and out[15] is set to 0.

When load=1 and in[8]=1 CSX goes high and DCX=in[9] without transmission of any bit.

When load16=1 transmission of word in[15:0] is initiated. CSX is goes low (and stays low even when transmission is completed). DCX is set to 1 (data). After 32 clock cycles transmission is completed and out[15] is set to 0.

### Proposed Implementation

Use a `Bit` to store the state (0 = ready, 1 = busy) which is output to out[15]. Another two `Bit` store the state of DCX and CSX. Use a counter `PC` to count from 0 to 15 or 31 according to load/load16. Finally we need two connected `BitShift8L`. They will be loaded with the byte in[7:0] or the word in[15:0] to be send.  After 8/16 bits are transmitted the module cleares out[15].

![](LCD.png)

### Memory map

The special function register `LCD` is mapped to memory map of HACK according to:

| address   | I/O device | R/W | function                            |
| --------- | ---------- | --- | ----------------------------------- |
| 4104      | LCD        | W   | start transmittion of byte in[7:0]  |
| 4105      | LCD        | W   | start transmittion of word in[15:0] |
| 4104/4105 | LCD        | R   | out[15]=1 busy, out[15]=0 idle      |

### LCD in real hardware

The board MO-LCD2.8RTP comes with a 2.8 inch LCD screen controlled by a controller chip ILI8341V. MOD-LCD2.8RTP must be connected to iCE40HX1K-EVB with 6 jumper wire cables: +3.3V, GND plus 4 data wires according to `iCE40HX1K-EVB.pcf` (Compare with schematic [iCE40HX1K_EVB](../../doc/iCE40HX1K-EVB_Rev_B.pdf) and [MOD-LCD2.8RTP_RevB.pdf](../../doc/MOD-LCD2.8RTP_RevB.pdf).

```
set_io LCD_DCX 1        # PIO3_1A connected to pin 5 of GPIO1
set_io LCD_SDO 2        # PIO3_1B connected to pin 7 of GPIO1
set_io LCD_SCK 3        # PIO3_2A connected to pin 9 of GPIO1
set_io LCD_CSX 4        # PIO3_2B connected to pin 11 of GPIO1
```

| wire    | iCE40HX1K-EVB (GPIO1) | MOD-LCD2.8RTP (UEXT) |
| ------- | --------------------- | -------------------- |
| +3.3V   | 3                     | 1 +3.3V              |
| GND     | 4                     | 2 GND                |
| LCD_DCX | 5                     | 7 D/C                |
| LCD_SDO | 7                     | 8 MOSI               |
| LCD_SCK | 9                     | 9 SCK                |
| LCD_CSX | 11                    | 11 CS                |

***

### Project

* Implement `LCD.v` and test with testbench:
  
  ```
  $ cd 06_LCD
  $ apio clean
  $ apio sim
  ```

* Compare output `OUT` of special chip`LCD` with `CMP`.
  
  ![](LCD_tb.png)

* Add special function register`LCD` to `HACK` at memory addresses 4104/4105 and upload to iCE40HX1K-EVB with the bootloader boot.asm preloaded into ROM
  
  ```
  $ cd ../05_GO
  $ make
  $ cd ../00_HACK
  $ apio clean
  $ apio upload
  ```

* Proceed to `07_Operating_System` and implement the driver class `Screen.jack` that sends command over `LCD` the controller chip ILI9341V on MOD-LCD2.8RTP