84PCSE:LCD Controller

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Quick Specs

8-bit RGB palette where the high and low bytes are the same. RGB is the normal mode. Row is the high nibble 0-F, column is the low nibble 0-F.
8-bit BGR palette where the high and low bytes are the same.


Like the old LCD controller, the new color controller is controlled by ports 10h and 11h. The LCD controller wants 16- or 18-bit data, but the Z80 only does 8-bit I/O, so each read or write takes TWO operations. The controller expects them to be in big-endian order, i.e. to output 1234h, you write 12h first, then write 34h to the SAME port. Writes to port 10h set the current "register". You need to send 16-bits to 10h at a time, even though there are no registers above 0FFh; every time you set the current register, send a dummy zero first, or alternatively, send the same byte twice. Reading 10h probably returns some kind of status information (more information needed). Reading and writing to 11h reads or writes to or from a register.

Therefore, to send the LCD a command, you first send two bytes to port 10h to set the current register. Then, you send two bytes to write the data. Similarly, to read, write the register number to 10h, and then read twice from 11h. You should be able to read-modify-write without resending the register number.

To send graphics to the LCD, set the column and row address registers, and then send the data serially to register #22h. You do not need to write 00 22h to port 10h after every byte.


In this document, the word "cursor" refers to the LCD controller's current reading or writing location on the screen; that is, the current row and column set by registers 20h and 21h.

(For those following along with the data sheet: Like before, the X/Y plane is flipped in the data sheet documentation. Specifically, the the screen is rotated 90 degrees from the way the manufacturer expects, so "horizontal" and "vertical" refer to the OTHER, i.e. horizontal means up and down on the screen. Also, "up" and "down" are switched with "left" and "right". Also, the auto-increment behavior in hardware is rotated 90 degrees clockwise from the register 0x03 diagram. It also suggests that the manufacturer expects the screen to be in landscape mode, which is wrong.)

To resolve potential CONFUSION about the meaning of the words "horizontal", "vertical", "up", "down", "left", "right", "X", and "Y", (see above paragraph) this document will use the terms "row" and "Y" to refer to the up/down direction positioning of the cursor on the actual calculator; similarly, "column" and "X" refer to the left/right axis. Additionally, as is standard for computer screens, the X=0 position is at the left side, and X+ is pointing to the right; and moreover, Y=0 is at the top, and Y+ points DOWN.


Like the old B&W LCD controller, this one has an internal cursor (the data sheet calls it the GRAM address) that determines where data written or read goes. Unlike the old controller, setting the row register will cause the column pointer to reset to the last value written, and vice versa. For example, if you set the row to 1, the column to 2, write a pixel so the column is now 3, and then set the row to 5, the column will not remain at 3, but revert to 2. (If you then set the column to 10, the row remains at 5, because 5 is the last value you wrote.)

So, port 10h:

  • Writing sets the index for the IR register
  • Reading reads an internal status code
  • Write four zeros to sync for multibyte transfers

Port 11h:

  • Writing sets a control register value or writes to GRAM (auto-buffered to WRD)
  • Reading reads from GRAM through the buffered RDR register (so a dummy read (16-bits!) is required before the data are valid, just like before)

TI always uses the 16-bit color mode. They also always seem to set BGR color order, even though the color data actually has red as the high bits, and blue as the low bits. (Perhaps it's "BGR" going form low-to-high bits, even though we write bits high-to-low.)

If you read the data sheet, the interface mode is the I80 8-bit mode.


To make life a little less terrible, the LCD controller supports setting a "window" into which the cursor is confined. In this window, if moving to the next pixel---whichever direction that may be---would move the cursor outside the bounds of the window, the cursor will instead move to the start of the next appropriate row or column, as determined by the entry mode, eventually wrapping back to the start of the window. This makes it easier to write sprites and do tiny animations. Windowing is always active, so it's something you must keep track of. Furthermore, you must set the cursor to inside the window when you change it, or else the screen will go totally wonky and display garbage when you try to write pixels to it.

Partial Image Mode

This has the potential to be quite useful. In particular, it allows a hacked 160x240 mode in which each pixel is twice as wide as normal. Somebody should probably add more information on this.

Panic Mode

If you do something the LCD controller finds particularly adverse (like set the cursor to be outside of the window bounds and try to write pixels), the LCD controller will display garbage lines everywhere. It will not operate normally again until you perform the power-off and power-on sequences.

Power Control

The B&W screen can be initialized with just half-a-dozen writes. The color screen is much more complicated. Power-on and power-off both require many writes with minimum wait times.

Be aware! The LCD controller is not connected to the LCD backlight controller. They are separate hardware, and operate independently. The LCD controller can be on without the backlight being on (you can't see anything except if you shine a very, very bright light directly on the screen), and the backlight can be on with LCD controller off. Port 3A controls the LCD backlight (among other things).

Power On

Key: shows the specific values TI gives to fields, check the documentation for
Binary: (- means zero & field is not defined)
    54321098 76543210
Port	Value	Purpose

On hard boot:

07	0000	Reset Disp.Ctrl.1: LCD scanning, command processing off
10	07F1	Reset Pwr.Ctrl.1: Start RC oscillator, set voltages
    ---0-111 1111--01	

Device soft-power on:
    54321098 76543210

01	0000	Reset Out.Ctrl.1: Ensure scan directions are not reversed
02	0200	LCD Driving Control: Sets inversion mode=line inversion and
    ------10 --------	disables it
03	1038	Init. Entry Mode: Cursor moves up/down, down, left, disable
    00-1---- 0-111---	auto-origin set for windows, BGR order, 16-bit color
08	0202	Set front & back porches: 2 blank lines top & bottom
    ----0010 ----0010	
09	0000	Reset Disp.Ctrl.3: Resets scanning stuff and off-screen voltage
0A	0000	Disp.Ctrl.4: No FMARK
0C	0000	RGB Disp.: Off
0D	0000	FMARK position: Off
60	2700	Driver Output Ctrl. 2
    ??100111 00000000	
61	0001	Base Image Display Ctrl: Use color inversion, no vertical
			scroll, reset voltage in non-display level
6A	0000	Reset Vertical Scroll Ctrl.

WAIT A WHILE (40 ms is good)

10	1190	Init Pwr.Ctrl.1: Exit standby, fiddle with voltages, enable
    ---1-001 1001--00	voltage booster
11	0227	Pwr.Ctrl.2: Configure voltages
    -----010 -010-111	


12	008C	Pwr.Ctrl.3: More voltages
    -------- 1--01100	


13	1800	Pwr.Ctrl.4: Take a wild guess
    ---11000 --------	
29	0030	Pwr.Ctrl.7: I'm not an LCD engineer, don't ask me.
    -------- --110000	
2B	000B	Set frame rate to 70
    -------- ----1011	


30	0000	Gamma Control 1: I really have idea about these.  Touching them
			may or may not make things explode.
31	0305	Gamma Control 2
32	0002	Gamma Control 3
35	0301	Gamma Control 4
36	0004	Gamma Control 5
37	0507	Gamma Control 6
38	0204	Gamma Control 7
39	0707	Gamma Control 8
3C	0103	Gamma Control 9
3D	0004	Gamma Control 10
50	0000	Horiz.Win.Start: 0
51	00EF	Horiz.Win.End: 239 = 240-1
52	0000	Vert.Win.Start: 0
53	013F	Vert.Win.End: 319 = 320-1


07	0133	Disp.Ctrl.1: LCD scan & light on, ready to enter standby
    --00---1 --110-11	No partial image

Power Off

Powering down the LCD controller is a lot easier. Just follow this sequence.

  • Write 0 to register 7 (lrDispCtrl1)
  • Wait
  • Write 07F0 to 10h (lrPwrCtrl)
  • Wait
  • Write 07F1 to 10h

Register List

This is a list of all the LCD's registers, what each bit does (if anything), and the values the OS expects for normal operation, so you can hopefully return the screen to normal after you're done screwing things up.

You should probably not screw with the power and scanning control registers. The screen might catch on fire, or cause the screen to fade over time, or just stop working. Remember, some of said registers directly control the internal voltages used in the controller.

00: ID Code

Reads: 9335h

01: Driver Output Control

Default: 0000h

Bit    Default    Description
8 0 Set to reverse row scan direction (i.e. upside-down mode). This only flips subsequent writes, not what's already on the screen.
10 0 Set for interlaced output

02: LCD Driving Control

Default: 0200h

Bit    Default    Description
8 0 EOR: Set with B/C = 1 to set line inversion
9 1 B/C: 0 = Frame/Field inversion, 1 = lin inversion

Comments: This seems to have no effect?

03: Entry Mode

Default: 1038h

Bit    Default    Description
3 1 AM: Cursor direction. Set = L/R, reset = U/D. After every pixel, the cursor moves either U/D or L/R.

If set to L/R (1), after every pixel the cursor moves left (bit 5=0) or right (b5=1). At the end of the row, the cursor moves up (b4=0) or down (b4=1).

If AM is set to U/D, after every pixel, the cursor moves up (b4=0) or down (b4=1). At the end of each column, the cursor moves left (b5=0) or right (b5=1).

At the end of every row or column, the cursor resets to the start of the next line, where ever the current window setting puts it.

4 1 Vertical increment/decrement: Set = increment
5 1 Horizontal increment/decrement: Set = increment
7 0 ORG: The controller's wording suggests that if this is set, then the cursor seeks to the corner of the window when the window is set, but this appears to be wrong?
12 1 BGR: If this is set, the "red" and "blue" channels are swapped both when writing pixels to GRAM, and when reading pixels from GRAM. Note that this doesn't affect the appearance of existing pixels.
14 0 DFM: If reset, each 3 writes with TRI set are packed. If set, each 3 writes with TRI set are unpacked.
15 0 TRI: If set, 3 writes are required for every pixel (of which 18 bits are used, allowing up to 218 distinct colors to be displayed). Note that unlike the BGR bit, TRI only affects output operations, not input operations.

The display has three color modes:

TRI    DFM    Transfer Mode
0 any 16-bit color, packed values, MSB first (big endian)
1 0 18-bit color, packed values, R[5:4] low bits of first transfer
1 1 18-bit color, unpacked values, uses high 6 bits, low two bits ignored

For example, to draw an orange pixel (R=100%, G=50%, B=0%) in TRI=0/BGR=1 mode, you would write 11111011b, 11100000b. In TRI=1/DFM=0/BGR=1 mode, you would write 00000011b, 11110111b, 11000000b. In TRI=1/DFM=1/BGR=1 mode, you would write 11111100b, 01111100b, 00000000b.

05: 16-bit Data Format Selection

The ILI9335 documentation is wrong about this register. It claims that it controls how the least-significant bits of the red and blue channels are determined when TRI=0. Experiments, however, have shown that the mode described as "EPF=10" is always used, regardless of the value of R05. In this mode, the most significant bit is copied into the least significant bit - or in other words, the input values are multiplied by 63/31 and rounded to the nearest integer.

(For reference, the documentation claims that mode 00 sets the least significant bits to 0; mode 01 sets the least significant bits to 1; mode 10 does as described above; and mode 11 does something not-completely-explained based on whether the red and blue values are equal.)

If this register has any effect, it's unknown.

07: Display Control 1

Default: 0133h

Bit    Default    Description
0 1 D0: Turn off scanning??
1 1 D1: Turn off LCD??
3 0 CL: Set for 8-colors mode
4 1 DTE: Set for normal operation
5 1 GON: Set for normal operation
8 1 BASEE: Set to keep LCD controller active even in standby/sleep
12 0 PTDE0: Set to enable partial image 1
13 0 PTDE1: Set to enable partial image 2

08: Display Control 2

Default: 0202h

You probably shouldn't muck with this field.

Bit    Default    Description
3:0 2 BP: Number of lines to skip after after VSYNC
11:8 2 FP: Number of lines to skip after finishing LCD scan

Neither may be set to 0, 1, or more than 128, and must total less than or equal to 256.

09: Display Control 3

Default: 0000h

You probably shouldn't muck with this field.

Bit    Default    Description
3:0 0 ISC: Scan cycle period = ISC*2-1 frames
4 0 PTG0: Do not set this bit
5 0 PTG1: Set for interval scan
10:8 0 PTS: Output voltage when scanning in non-display area

0A: Display Control 4

Default: 0000h

Probably useless to us

Bit    Default    Description
2:0 0 FMARK interval, valid values are 0, 1, 3, 5
3 0 MKARKOE: Enables FMARK

0C: RGB Display Interface Control 1

Default: 0000h

Probably useless to us

Bit    Default    Description
1:0 0 RIM
5:4 0 DM
8 0 RM
14:12 0 ENC

0D: Frame Maker Position

Default: 0000h

Probably useless to us

Bit    Default    Description
8:0 0 FMP: Sets when the FMARK pulse is output

0F: RGB Display Interface Control 2

Default: 0000h

Probably useless to us, TI doesn't initalize it

Bit    Default    Description

10: Power Control 1

Default: 1190h

You probably shouldn't muck with this field.

Bit    Default    Description
0 0 STB: Set=sleep mode (RC oscillator still active)
1 0 SLP: Set=standby mode (GRAM preserved)

In STB or SLP, no commands except exit STB or SLP are accepted

6:4 1 AP: OP amp adjust
7 1 APE: Set to enable power supply startup
10:8 1 BT: Voltage step-up adjust
12 1 SAP: Set=source driver enabled, boot with this=0 then set to 1

after LCD power supply is active

11: Power Control 2

Default: 0227h

You probably shouldn't muck with this field.

Bit    Default    Description
2:0 VC
6:4 DC0
10:8 DC1

12: Power Control 3

Default: 008Ch

You probably shouldn't muck with this field.

Bit    Default    Description
3:0 VRH

13: Power Control 4

Default: 1800h

You probably shouldn't muck with this field.

Bit    Default    Description
12:8 VDV

20: Cursor Row

The datasheet calls this the "Horizontal GRAM Address" , but it sets the up/down position of the cursor because the display is on its side.

21: Cursor Column

Sets the left/right position of the cursor. NOTA BENE: Setting one register will cause the other to revert to its previous value; see Overview, above.

22: GRAM

This is the register that you use to actually send and read pixels.

When reading, a dummy read is required before a cursor change takes effect; i.e., after writing 20 and 21, do a 16-bit dummy read before saving the actual data.

Reading does not appear to update the cursor, so you can do a read-modify-write type operation, which might be useful for masking or implementing gratuitous transparency effects.

29: Power Control 7

Default: 0030h

You probably shouldn't muck with this field.

Bit    Default    Description
5:0 VCM

2B: Frame Rate and Color Control

Default: 0000Bh

Bit    Default    Description
3:0 0Bh Frame rates, 0-15: 31, 33, 34, 36, 39, 41, 44, 48, 52, 57, 62,

69, 78, 89, undefined, undefined

30-3D: Gamma Control

You probably shouldn't muck with these fields.

Default values:

Register    Value    Description
30 0000 Gamma Control 1
31 0305 Gamma Control 2
32 0002 Gamma Control 3
35 0301 Gamma Control 4
36 0004 Gamma Control 5
37 0507 Gamma Control 6
38 0204 Gamma Control 7
39 0707 Gamma Control 8
3C 0103 Gamma Control 9
3D 0004 Gamma Control 10

50: Window Horizontal Address Start

Default: 0000h

Defines leftmost position of window, inclusive. Remember that it's the actually the top of the window on the calculator.

51: Window Horizontal Address End

Default: 00EFh

Exactly what you think. This is inclusive, like port 50, so if your sprite starts on column 0 and is 10 pixels wide, do not add 10 to 0 to get 10. The number you want is 9.

52: Window Vertical Address Start

Default: 0000h

53: Window Vertical Address End

Default: 013Fh

60: Gate Scan Control

Default: 2700

Bit    Default    Description
5:0 0 SCN: Sets the gate line from which the gate driver starts to scan.
13:8 27h NL: Sets the number of lines to drive the LCD at an interval of 8 lines. In other words, it tells the LCD controller how big the screen really is.
15 0 GS: Gate scan direction. Setting this will cause left/right mirroring.

61: Base Image Display Control

Default: 0001h

Bit    Default    Description
0 1 REV: Set=enable grayscale inversion
1 0 VLE: Vertical scroll enable.
2 0 NDL: Sets the output level in the non-display area

6A: Vertical Scroll Control

Default: 0000

Because the LCD is rotated, this actually scrolls horizontally.

Partial image display is not affected by this.

Bit    Default    Description
8:0 0000 Sets the line to start displaying from.

80: Partial Image 1 Display Position

81: Partial Image 1 Start Line

82: Partial Image 1 End Line

83: Partial Image 2 Display Position

84: Partial Image 2 Start Line

85: Partial Image 2 End Line

90: Panel Interface Control 1

Default: 0000

92: Panel Interface Control 2

Default: 0600h

No, I don't know what happened to Panel Interface Control 3. It's totally missing from the datasheet.

95: Panel Interface Control 4

Default: 0200

97: Panel Interface Control 5

Default: 0C00