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HT56R22 Datasheet(PDF) 23 Page - Holtek Semiconductor Inc |
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HT56R22 Datasheet(HTML) 23 Page - Holtek Semiconductor Inc |
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23 / 127 page  HT56R22/HT56R23/HT56R24/HT56R25/HT56R26 Rev. 1.30 23 December 26, 2014 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 writeable 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. 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 both Bank 0 and Bank 1. Any unused Data Memory locations between these special function registers and the point where the General Purpose Memory begins is reserved and attempting to read data from these locations will re- turn 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 access 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. MP0 can only be used to indirectly address data in Bank 0 while MP1 can be used to address data in Bank 0 and Bank1. When any operation to the relevant Indi- rect Addressing Registers is carried out, the actual ad- dress that the microcontroller is directed to, is the address specified by the related Memory Pointer. Note that for the HT56R22 device, bit 7 of the Memory Pointers is not required to address the full memory space. When bit 7 of the Memory Pointers for this device is read, a value of ²1² will be returned. Note that indirect addressing using MP1 and IAR1 must be used to access any data in Bank 1. The following example shows how to clear a section of four Data Memory locations already de- fined as locations adres1 to adres4. · 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. |
Similar Part No. - HT56R22_14 |
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Similar Description - HT56R22_14 |
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