Download Notes On Using T6963-based Displays

Notes On Using T6963based Displays
This document contains some notes on pro­
gramming and using LC displays based on the
Toshiba T6963 display controller.
Selecting the display
When deciding which display to buy these are
some important selection criteria:
1. The display should have a negative
voltage generator on-board.
Frequently asked questions
While searching for more information on the
web I frequently read these questions:
you see excess dots from the next character in
the last two pixel columns.
On displays where the horizontal resolution is
not a multiple of 6 the display RAM should be
filled with one space character in the last (partly
visible column), but the display should be con­
figured to wrap on fully visible columns.
Example: On 128x64 configure 21 columns, but
write a space to RAM after each 21st character.
With 6x8 font, graphic RAM has to be treated
differently as well. From each byte of graphic
RAM only the lower 6 bits are used.
I have read several people asking for “des­
troyed” images as they try to write the bytes of
an image to the display and only get garbage.
The figure below shows image bytes written to
the display with 8x8 font selected.
How big can the display be?
The answer to this question is two-fold: First
there is a maximum number of dots the control­
ler can handle.
The controller can handle up to 256 rows
(defined by pins DUAL, MDS, MD0, MD1) and
up to 640 columns (defined by pins MD2, MD3
and FS0, FS1).
Next the oscillator frequency puts a limit on the
screen size. Figure 2 in the data-sheet shows a
table which sizes can be achieved by which fre­
quency.
Figure 1: Image bytes with 8x8 font
The figure below shows image bytes written to
the display with 6x8 font selected.
Font size
The T6963 supports selecting different sizes of
the internal font: 5x8, 6x8, 7x8, 8x8 (pins FS0,
FS1). But many displays provide only one pin to
select between 6x8 and 8x8.
The font size affects how the controller treats
bytes stored in RAM. Example:
Display size is 128 x 64 dots. With 8x8 font this
gives 16 x 8 characters.
However, the font size also affects graphic
RAM. With 8x8 font each “column” represents 8
dots. Therefore one byte is exactly 8 dots.
With 6x8 font everything changes. First you get
21,3 x 8 characters (128 / 6 = 21,3). As text
RAM is continuous and the controller simply
starts a new line after the configured column
Figure 2: Image bytes with 6x8 font
Notice that some pixels are missing (the two
leftmost bits of each byte) and the image is re­
peated on the right and garbage appears in the
lower right corner.
If the font is configured to 6x8 each 3 bytes (8
bits) of image data have to be split to 4 bytes of
graphic RAM (each using 6 bits).
© 2011, Markus Dolze <[email protected]>
Crystalfontz CFAG12864DYYH-TZ
For my tests I use the CFAG12864D-YYH-TZ, a
T6963-based display from Crystalfontz. Figure
3 shows the back-side of the display and sever­
al function blocks on it:
•
The chip under the white label is the
T6963.
•
Three display row / column drivers
•
32KB graphic RAM (note the data-sheet
states it only has 8K RAM)
•
6MHz oscillator circuit
•
Several solder jumpers to configure the
pin-out
•
The reset circuit is not populated.
•
Negative voltage generator with softstart circuit
Both (no LCD bias on power-up and on HALT)
are requirements in the T6963's data-sheet).
The effect of the soft-start circuit can be seen in
figure 4.
Figure 4: voltage level on Vee
Note: Vee was connected by a variable resistor
to pin 1 (N.V.) and Vdd (as recommended by
the data-sheet). It should probably better be
Figure 3: Crystalfontz CFAG12864D-YYH-TZ
The display is equipped with a negative voltage
generator that is triggered by the T6963's HALT
signal. That is, power to the LCD is disabled if
the controller is stopped. Also a soft-start circuit
consisting of a MOSFET and some resistors /
capacitors is available that delay power to the
LCD on power-up.
connected to Vss (GND) as there is a small (1
V, 40 us) spike of positive voltage. Within 2 ms
the negative voltage slowly reaches its desired
value.
© 2011, Markus Dolze <[email protected]>