Chapter 1 Hardware Structure
LCD Memory
The data to be displayed on the LCD is also stored in an area of fully accessible Data Memory. By
writing to this area of RAM, the LCD display output can be directly controlled by the application pro-
gram. As the LCD Memory exists in Bank 1, but have addresses which map into the General Pur-
pose Data Memory, it is necessary to first ensure that the Bank Pointer is set to the value
²01H²
before accessing the LCD Memory. The LCD Memory can only be accessed indirectly using the
Memory Pointer MP1 and the indirect addressing register IAR1. When the Bank Pointer is set to
Bank 1 to access the LCD Data Memory, if any addresses with a value less than
²40H²
are read,
the General Purpose Memory in Bank 0 will be accessed. Also, if the Bank Pointer is set to Bank 1,
if any addresses higher than the last address in Bank 1 are read, then a value of
²00H²
will be re-
turned.
The following diagram shows the LCD Memory Map for the LCD Type microcontroller:
H T 4 9 R 3 0 A -1
H T 4 9 C 3 0 -1
H T 4 9 C 3 0 L
4 0 H
5 2 H
4 0 H
L C D M e m o ry
B a n k 1
6 0 H
L C D M e m o ry
B a n k 1
6 8 H
H T 4 9 R 5 0 A -1
H T 4 9 C 5 0 -1
H T 4 9 C 5 0 L
4 0 H
H T 4 9 R 7 0 A -1
H T 4 9 C 7 0 -1
H T 4 9 C 7 0 L
4 0 H
L C D M e m o ry
B a n k 1
6 F H
H T 4 9 R U 8 0
H T 4 9 C U 8 0
L C D M e m o ry
B a n k 1
Special Function Registers
To ensure successful operation of the microcontroller, certain internal registers are implemented
in the Data Memory area. These registers ensure correct operation of internal functions such as
timers, interrupts, etc., as well as external functions such as I/O data control. The location of these
registers within the Data Memory begins at the address
²00H².
Any unused Data Memory loca-
tions between these special function registers and the point where the General Purpose Memory
begins is reserved for future expansion purposes, attempting to read data from these locations will
return a value of
²00H².
Indirect Addressing Registers
-
IAR0, IAR1
The method of indirect addressing allows data manipulation using Memory Pointers instead of the
usual direct memory addressing method where the actual memory address is defined. Any action
on the Indirect Addressing Registers will result in corresponding read/write operations to the mem-
ory location specified by the corresponding Memory Pointer. All devices in the LCD range of
microcontrollers contain two indirect addressing registers known as IAR0 and IAR1 and two Mem-
ory Pointers MP0 and MP1. Note that these Indirect Addressing Registers are not physically imple-
mented and that reading the Indirect Addressing Registers indirectly will return a result of
²00H²
and writing to the registers indirectly will result in no operation.
37
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