HT46R0664 datasheet(22/92 Pages) HOLTEK

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HT46R0664

Enhanced A/D+LCD Type 8-Bit OTP MCU

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.

Bank Pointer – BP

The Data Memory is divided into three Banks, known as Bank 0, Bank1 and Bank 2. A Bank

Pointer, which is bit 0~1 of the Bank Pointer register is used to select the required Data Memory

bank. Only data in Bank 0 can be directly addressed as data in Bank 1 and Bank2 must be

indirectly addressed using Memory Pointer MP1 and Indirect Addressing Register IAR1. Using

Memory Pointer MP0 and Indirect Addressing Register IAR0 will always access data from Bank 0,

irrespective of the value of the Bank Pointer. Memory Pointer MP1 and Indirect Addressing Register

IAR1 can indirectly address data in Bank 0, Bank 1, or Bank 2 depending upon the value of the

Bank Pointer. The Data Memory is initialised to Bank 0 after a reset, except for the WDT time-out

reset in the Idle/Sleep Mode, in which case, the Data Memory bank remains unaffected. It should be

noted that Special Function Data Memory is not affected by the bank selection, which means that

the Special Function Registers can be accessed from Bank 0, Bank1 or Bank 2. Directly addressing

the Data Memory will always result in Bank 0 being accessed irrespective of the value of the Bank

Pointer.

BP Register

Bit

Name

—

DMBP1

DMBP0

R/W

—

R/W

POR

—

Bit 7~2

Unimplemented, read as “0”

Bit 1~0

DMBP1, DMBP0: Data memory bank point

00: bank 0

01: bank 1

10: bank 2

11: undefined

Program Counter Low Register – PCL

To provide additional program control functions, the low byte of the Program Counter is made

accessible to programmers by locating it within the Special Purpose area of the Data Memory. By

manipulating this register, direct jumps to other program locations are easily implemented. Loading

a value directly into this PCL register will cause a jump to the specified Program Memory location,

however as the register is only 8-bit wide only jumps within the current Program Memory page are

permitted. When such operations are used, note that a dummy cycle will be inserted.

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