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HT49CA1 Datasheet(PDF) 11 Page - Holtek Semiconductor Inc |
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HT49CA1 Datasheet(HTML) 11 Page - Holtek Semiconductor Inc |
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11 / 57 page  HT49RA1/HT49CA1 Rev. 1.10 11 March 30, 2014 the LCD Data Memory, will be in an unknown condition, the programmer must therefore ensure that the Data Memory is properly initialised. 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 pro- gram 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. As the General Purpose Data Memory exists in Bank 0, it is 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 1must be addressed indirectly using the Memory Pointer MP1 and the indirect addressing register IAR1. Any direct addressing or any indirect ad- dressing using MP0 and IAR0 will always result in data from Bank 0 being accessed. Special Purpose Data Memory This area of Data Memory is where registers, necessary for the correct operation of the microcontroller, are stored. Most of the registers are both readable and writable but some are protected and are readable only, the details of which are located under the relevant Spe- cial Function Register section. Note that for locations that are unused, any read instruction to these addresses will return the value ²00H². 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 con- trolled by the application program. As the LCD Memory exists in Bank 1, but have addresses which map into the Bank 0 Data Memory, it is necessary to first ensure that the Bank Pointer is set to the value 01H before accessing the LCD Memory. The LCD Memory can only be ac- cessed 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. 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 be- gins at the address ²00H². Any unused Data Memory lo- cations between these special function registers and the point where the General Purpose Memory begins is re- served for future expansion purposes, attempting to read data from these locations will return a value of ²00H². Indirect Addressing Register - IAR0, IAR1 The IAR0 and IAR1 registers, located at Data Memory addresses ²00H² and ²02H², are not physically imple- mented. These special function registers allows what is known as indirect addressing, which permits data ma- nipulation using Memory Pointers instead of the usual direct memory addressing method where the actual memory address is defined. Any actions on the IAR0 and IAR1 registers will result in corresponding read/write operations to the memory locations specified by the Memory Pointers MP0 and MP1. Reading the IAR0 and IAR1 registers indirectly will return a result of ²00H² and writing to the register indirectly will result in no operation. : U n u s e d , r e a d a s " 0 0 " I A R 0 M P 0 I A R 1 M P 1 B P A C C P C L T B L P T B L H R T C C S T A T U S I N T C 0 T M R 0 T M R 0 C T M R 1 H T M R 1 L T M R 1 C P A P B P C P C C P D I N T C 1 L C D C Special Purpose Data Memory |
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