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HT46R01B-1 Datasheet(PDF) 16 Page - Holtek Semiconductor Inc |
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HT46R01B-1 Datasheet(HTML) 16 Page - Holtek Semiconductor Inc |
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16 / 71 page  HT46R01B-1/HT46R01N-1 HT48R01B-1/HT48R01N-1 Rev.1.00 16 June 9, 2011 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 and are mapped into Bank 0. Any unused Data Memory locations between these spe- cial function registers and the point where the General Purpose Memory begins is reserved and attempting to read data from these locations will return a value of ²00H². Indirect Addressing Registers - IAR0, IAR1 The Indirect Addressing Registers, IAR0 and IAR1, al- though having their locations in normal RAM register space, do not actually physically exist as normal regis- ters. The method of indirect addressing for RAM data manipulation uses these Indirect Addressing Registers and Memory Pointers, in contrast to direct memory ad- dressing, where the actual memory address is speci- fied. Actions on the IAR0 and IAR1 registers will result in no actual read or write operation to these registers but rather to the memory location specified by their corre- sponding Memory Pointer, MP0 or MP1. Acting as a pair, IAR0 with MP0 and IAR1 with MP1 can together ac- cess data from the Data Memory. As the Indirect Ad- dressing Registers are not physically implemented, reading the Indirect Addressing Registers indirectly will return a result of ²00H² and writing to the registers indi- rectly will result in no operation. Memory Pointers - MP0, MP1 Two Memory Pointers, known as MP0 and MP1 are pro- vided. These Memory Pointers are physically imple- mented in the Data Memory and can be manipulated in the same way as normal registers providing a conve- nient way with which to indirectly address and track data. When any operation to the relevant Indirect Ad- dressing Registers is carried out, the actual address that the microcontroller is directed to, is the address speci- fied by the related Memory Pointer. The following exam- ple shows how to clear a section of four Data Memory locations already defined as locations adres1 to adres4. Accumulator - ACC The Accumulator is central to the operation of any microcontroller and is closely related with operations carried out by the ALU. The Accumulator is the place where all intermediate results from the ALU are stored. Without the Accumulator it would be necessary to write the result of each calculation or logical operation such as addition, subtraction, shift, etc., to the Data Memory resulting in higher programming and timing overheads. Data transfer operations usually involve the temporary storage function of the Accumulator; for example, when transferring data between one user defined register and another, it is necessary to do this by passing the data through the Accumulator as no direct transfer between two registers is permitted. · Indirect Addressing Program Example data .section ¢data¢ adres1 db ? adres2 db ? adres3 db ? adres4 db ? block db ? code .section at 0 code org 00h start: mov a,04h ; setup size of block mov block,a mov a,offset adres1 ; Accumulator loaded with first RAM address mov mp0,a ; setup memory pointer with first RAM address loop: clr IAR0 ; clear the data at address defined by MP0 inc mp0 ; increment memory pointer sdz block ; check if last memory location has been cleared jmp loop continue: The important point to note here is that in the example shown above, no reference is made to specific Data Memory addresses. |
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