HT45R22E Holtek Semiconductor, HT45R22E Datasheet - Page 14

• Manufacturer Part Number: HT45R22E
• Description: Remote Type 8-bit OTP MCU
• Manufacturer: Holtek Semiconductor

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 00H .
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
locations of these registers within the Data Memory be-
gin at the address 00H . Any unused Data Memory lo-
cations between these special function registers and the
point where the General Purpose Memory begins is re-
served and attempting to read data from these locations
will return a value of 00H .
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 00H 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
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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 specified
by the related Memory Pointer. The following example
shows how to clear a section of four Data Memory loca-
tions already defined as locations adres1 to adres4.
Special Purpose Data Memory
HT45R22E
March 17, 2010
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