HT45R35 datasheet(9/59 Pages) HOLTEK

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HT45R35

Rev. 1.30

May 14, 2010

Bank Pointer

- BP

When using instructions to access the general purpose

data memory in Bank 0 or Bank 1, it is necessary to en-

sure that the correct area is selected. The general pur-

pose data memory is sub-divided into two banks, Bank 0

and Bank 1 for this device. Selecting the correct data

memory area is achieved by using the bank pointer. If

data in Bank 0 or Bank 1 is to be accessed, the BP must

be set to the values

²00H² or ²01H² respectively, how-

ever, it must be noted that data in Bank 1 can only be ad-

dressed indirectly using the MP1 memory pointer and

the IAR1 indirect addressing register.

Any direct addressing or any indirect addressing using

MP0 and IAR0 will always result in data from Bank 0 be-

ing accessed. The data memory is initialized to Bank 0

after a reset, except for the WDT time-out reset in the

Power Down Mode, in which case, the data memory

bank remains unchanged.

It should be noted that the special function data memory

is not affected by the bank selection, which means that

the special function registers can be accessed from

within either Bank 0 or Bank 1.

Accumulator

The accumulator is closely related to ALU operations. It

is also mapped to location

²05H² of the data memory

and can carry out immediate data operations. The data

movement between two data memory locations must

pass through the accumulator.

Arithmetic and Logic Unit

- ALU

This circuit performs 8-bit arithmetic and logic opera-

tions. The ALU provides the following functions:

· Arithmetic operations

- ADD, ADC, SUB, SBC, DAA

· Logic operations

- AND, OR, XOR, CPL

· Rotation

- RL, RR, RLC, RRC

· Increment and Decrement

- INC, DEC

· Branch decision

- SZ, SNZ, SIZ, SDZ ....

The ALU not only saves the results of a data operation

but also changes the status register.

Status Register

- STATUS

This 8-bit register contains the zero flag (Z), carry flag

(C), auxiliary carry flag (AC), overflow flag (OV), power

down flag (PDF), and watchdog time-out flag (TO). It

also records the status information and controls the op-

eration sequence.

With the exception of the TO and PDF flags, bits in the

status register can be altered by instructions like most

other registers. Any data written into the status register

will not change the TO or PDF flag. In addition opera-

tions related to the status register may give different re-

sults from those intended. The TO flag can be affected

only by a system power-up, a WDT time-out or execut-

ing the

²CLR WDT² or ²HALT² instruction.

The PDF flag can be affected only by executing a

²HALT² or ²CLR WDT² instruction or a system

power-up.

The Z, OV, AC and C flags generally reflect the status of

the latest operations.

In addition, on entering the interrupt sequence or exe-

cuting the subroutine call, the status register will not be

pushed onto the stack automatically. If the contents of

the status are important and if the subroutine can cor-

rupt the status register, precautions must be taken to

save it properly.

Bit No.

Label

Function

C is set if the operation results in a carry during an addition operation or if a borrow does not

take place during a subtraction operation; otherwise C is cleared. C is also affected by a rotate

through carry instruction.

1AC

AC is set if the operation results in a carry out of the low nibbles in addition or no borrow from

the high nibble into the low nibble in subtraction; otherwise AC is cleared.

Z is set if the result of an arithmetic or logic operation is zero; otherwise Z is cleared.

3OV

OV is set if the operation results in a carry into the highest-order bit but not a carry out of the

highest-order bit, or vice versa; otherwise OV is cleared.

PDF

PDF is cleared by system power-up or executing the

²CLR WDT² instruction.

PDF is set by executing the

²HALT² instruction.

5TO

TO is cleared by system power-up or executing the

²CLR WDT² or ²HALT² instruction.

TO is set by a WDT time-out.

6~7

Unused bit, read as

²0²

Status (0AH) Register

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