HD44780 LCD operation

[LAJ5]

hi. can someone please help me? im using HD44780 LCD. i don't know why it is not working. a tested program was provided to us, proper connections and yet it doesn't diplayed anything. what seems to be the problem? im using z8microcontroller.

 

[Nigel Goodwin]

It's either connected wrong, it's faulty, or the program isn't correct - with faulty being by FAR the least likely option.

 

[DigiTan]

I would start by applying power and verifying the powerup test pattern works. The first row of characters will be darkened boxes, followed by a blank second row. If it remains blank, it's either a display fault, or you have the Vo pin set to minimum contrast. Otherwise, this is the startup sequence I use in my 4-bit displays. Keep in mind 4-bit mode uses pins Data4 thru Data7; with Data4 as the LSB. To "EXECUTE," I ground the ENable pin for 1us, then raise it back to Vdd.

---ON POWER UP
* RS pin grounded
* EN pin at Vcc
* R/W permanently grounded into write mode

---LCD INITIALIZE
* Hold 16.320ms (15ms minimum required)
* Send "03h" to LCD bus
* EXECUTE
* Hold 4.608ms (4.1 minimum required)
* EXECUTE
* Hold 128us
* EXECUTE
* Hold 128us
* Send "02h" to bus ("Function set" for using a 4 bit interface)
* EXECUTE
* Hold 128us

---LCD BUS WIDTH AND DISPLAY SIZE SETUP
* Send "02h" to bus ("Function Set" command)
* EXECUTE
* Hold 64us
* Send "04h" to bus (To indicate dual line display)
* EXECUTE
* Hold 64us

After that I send the remainder of command to power off the display, change cursor options, then tell the LCD to power on again. Basically all my holds are 10% longer than the minimum recommendation.

 

[ssylee]

wschroeder:

I've gotten your code working on my LCD. Again, I connected the data ports wrong, which resulted in not seeing anything on my LCD. How would I switch the position of the cursor? By using one of the command flashing functions in your code?

 

[Nigel Goodwin]

wschroeder:

I've gotten your code working on my LCD. Again, I connected the data ports wrong, which resulted in not seeing anything on my LCD. How would I switch the position of the cursor? By using one of the command flashing functions in your code?

All the commands are listed on the datasheet, and also in my tutorials - where I also provide subroutines to move the cursor (and various other common actions).

 

[wschroeder]

wschroeder:

I've gotten your code working on my LCD. Again, I connected the data ports wrong, which resulted in not seeing anything on my LCD. How would I switch the position of the cursor? By using one of the command flashing functions in your code?

The LCD4_CMD() is how you set the address for the cursor, and anything you write will show at that point. Remember that the LCD is setup to automatically advance the cursor position after a write.

Here are the starting addresses of the most common HD44780/compatible controllers. You can simply count across the screen from these addresses to find any point on a line.

2x16, 2x20, 2x24, 2x40 LCD Line Start Addresses + DDRAM Access:
LINE 1 = 0 + 128 = 128
LINE 2 = 64 + 128 = 192

If using a 4 line LCD, Line3 is a continuation of screen addresses from Line1, and Line4 is a continuation of addresses of Line2:

4x16 LCD Line Start Addresses + DDRAM Access
LINE 1 = 0 + 128 = 128
LINE 2 = 64 + 128 = 192
LINE 3 = 16 + 128 = 144
LINE 4 = 80 + 128 = 208

4x20 Line Start Addresses + DDRAM Access
LINE 1 = 0 + 128 = 128
LINE 2 = 64 + 128 = 192
LINE 3 = 20 + 128 = 148
LINE 4 = 84 + 128 = 212

128 (Setting Bit-7 of the Command Byte) is the additional Command requirement for accessing the DDRAM, also known as the read/write screen locations. So, if you want to set the cursor to Line 1 and and the 4th character, do something like this:

LCD4_CMD(131)