Chapter 1 Hardware Structure
Liquid Crystal Display (LCD) Driver
For large volume applications, which incorporate an LCD in their design, the use of a custom dis-
play rather than a more expensive character based display reduces costs significantly. However,
the corresponding signals required, which vary in both amplitude and time, to drive such a custom
display require many special considerations for proper LCD operation to occur. The Holtek LCD
Type MCU series, with their internal LCD signal generating circuitry and various configuration op-
tions, will automatically generate these time and amplitude varying signals to provide a means of
direct driving and easy interfacing to a range of custom LCDs.
LCD Memory
Each device in the LCD Type MCU series provides a specific area of Data Memory for the LCD
data. This data area is known as the LCD Memory. Any data written here will be automatically read
by the internal LCD driver circuits, which will in turn automatically generate the necessary LCD
driving signals. Therefore any data written into the LCD Memory will be immediately reflected into
the actual LCD display connected to the microcontroller. The start address of the LCD Memory is
40H for all devices in the LCD Type MCU series. However, as the LCD memory capacity provided
varies, dependent upon which device is chosen, the end address of the LCD Memory varies be-
tween 52H and 6FH.
As the LCD Data Memory addresses overlap those of the General Purpose Data Memory, the
LCD Data Memory is stored in its own memory data bank, which is different from that of the Gen-
eral Purpose Data Memory. With the exception of the HT49RU80/HT49CU80 devices, all the
other devices have their General Purpose Data Memory stored in a single Bank 0. For the
HT49RU80/HT49CU80 devices, the General Purpose Data Memory is stored in Bank 0, Bank 2
and Bank 3. For all devices, the LCD Data Memory is stored in Bank 1. The Data Memory Bank is
chosen by using the Bank Pointer, which is a special function register in the Data Memory, with the
name, BP. When the lowest two bits of the Bank Pointer have the binary value
²00²,
or additionally
²10²
or
²11²
for the HT49RU80/HT49CU80 devices, only the General Purpose Data Memory will
be accessed, no read or write actions to the LCD Memory will take place. To access the LCD Mem-
ory therefore requires first that Bank 1 is selected by setting the lowest two bits of the Bank Pointer
to the binary value
²01².
After this, the LCD Memory can then be accessed by using indirect ad-
dressing through the use of Memory Pointer MP1. With Bank 1 selected, then using MP1 to read
or write to the memory area, 40H~52H, 40H~60H, 40H~68H or 40H~6FH, depending upon which
device is chosen, will result in operations to the LCD Memory. Directly addressing the LCD Mem-
ory is not applicable and will result in a data access to the Bank 0 General Purpose Data Memory.
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