84PCSE:LCD Controller

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Quick Specs


Overview

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. 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.

NOTA BENE: IMPORTANT TERMINOLOGY:

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.

READ THE ABOVE OR YOU WILL HAVE BUGS!

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, and they always set BGR color order, for no good reason.

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


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: Driver Code

Reads 9335h

01: Driver Output Control 1

Default: 0000h

Bit    Default    Description
8 0 Set to reverse row scan direction (i.e. upside-down mode)
10 0 Set for interlaced output

02: LCD Driving Control

Default:

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:

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 set, this specifies BGR color channel order. TI uses this.
14 0 TRI: If set, 3 writes are required for every pixel.
15 0 DFM: If reset, the 3 writes are packed.

If set, the 3 writes are unpacked. (That is, write 1 byte red, 1 byte green, and finally 1 byte blue, or reverse for BGR.)

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

05: 16-bit Data Format Selection

TI does not appear ever to set a value for this register?

Bit    Default    Description
1:0 1 EPF: If set to 0, the low bit of red and blue is always zero.

If set to 1, the low bit of red and blue is always one.

If set to 2, the low bit of red and blue is copied from the high bit.

If set to 3, the low bit of red and blue is copied from the low bit of green.

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
0 DPL
1 EPL
3 HSPL
4 VSPL

Default:

Bit    Default    Description

Default:

Bit    Default    Description
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