Chapter 1 Hardware Structure
General Purpose Data Memory
All microcontroller programs require an area of read/write memory where temporary data can be
stored and retrieved for use later. It is this area of RAM memory that is known as General Purpose
Data Memory. This area of Data Memory is fully accessible by the user program for both read and
write operations. By using the
²SET
[m].i² and
²CLR
[m].i² instructions individual bits can be set or
reset under program control giving the user a large range of flexibility for bit manipulation in the
Data Memory. With the exception of the HT49RU80/HT49CU80, the General Purpose Data Mem-
ory exists in Bank 0. For the HT49RU80/HT49CU80, the General Purpose Data Memory exists in
three Banks, namely Bank 0, Bank 2 and Bank 3. It is therefore necessary to first ensure that the
Bank Pointer is set to the correct value before accessing the General Purpose Data Memory.
When the Bank Pointer is set to the value 01H, the LCD Memory will be accessed. Bank 1, Bank 2
or Bank 3 must be addressed indirectly using the Memory Pointer MP1 and the indirect address-
ing register IAR1. Any direct addressing or any indirect addressing using MP0 and IAR0 will al-
ways result in data from Bank 0 being accessed.
The following diagram shows the General Purpose Data Memory Organization Map for the LCD
Type microcontrollers:
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
2 0 H
2 0 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
2 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
H T 4 9 R U 8 0
H T 4 9 C U 8 0
4 0 H
8 0 H
B a n k 0
6 0 H
F F H
F F H
9 6 B y te s
B a n k 0
1 6 0 B y te s
F F H
B a n k 0
2 2 4 B y te s
F F H
: U n u s e d , re a d a s "0 0 "
B a n k 0
B a n k 2
B a n k 3
5 7 6 B y te s
Note
The 576 bytes of the General Purpose Data Memory in the HT49RU80/HT49CU80 devices are
stored in three individual memory banks, known as Bank 0, Bank 2 and Bank 3. Before reading or
writing to the General Purpose Data Memory it is essential to first ensure that the correct Data
Memory bank is selected by setting up the Bank Pointer. Bank 1, Bank 2 and Bank 3 can only be
addressed indirectly using MP1 and IAR1.
35
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