BS2824 Holtek Semiconductor Inc., BS2824 Datasheet - Page 19

• Manufacturer Part Number: BS2824
• Description: Touch Key Mcu
• Manufacturer: Holtek Semiconductor Inc.

Special Function Registers
Rev. 1.00
Special Purpose Data Memory
Indirect Addressing Registers - IAR0, IAR1
In the BS2868, the Data Memory is subdivided into two banks, which are selected using a Bank
Pointer. Only data in Bank 0 can be directly addressed, data in Bank 1 must be indirectly addressed.
Note:
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 Special Function
Register section. Note that for locations that are unused, any read instruction to these addresses will
return the value 00H .
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 begins at the address 00H 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
return a value of 00H .
The Indirect Addressing Registers, IAR0 and IAR1, although having their locations in normal RAM
register space, do not actually physically exist as normal registers. The method of indirect
addressing for RAM data manipulation uses these Indirect Addressing Registers and Memory
Pointers, in contrast to direct memory addressing, where the actual memory address is specified.
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 corresponding 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 Addressing Registers are not physically implemented, reading the
Indirect Addressing Registers indirectly will return a result of 00H and writing to the registers
indirectly will result in no operation.
Most of the Data Memory bits can be directly manipulated using the SET [m].i and CLR
[m].i with the exception of a few dedicated bits. The Data Memory can also be accessed
through the memory pointer registers.
Data Memory Structure
19
BS2824/BS2854/BS2868
Touch Key MCU
January 27, 2010