HT68F13 datasheet(25/161 Pages) HOLTEK

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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

transfer between two registers is permitted.

ProgramCounterLowRegister

- 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.

Look-upTableRegisters

- TBLP, TBHP, TBLH

These three special function registers are used to control operation of the look-up table which is stored

in the Program Memory. TBLP and TBHP are the table pointer and indicates the location where the

table data is located. Their value must be setup before any table read commands are executed. Their

value can be changed, for example using the

²INC² or ²DEC² instructions, allowing for easy table data

pointing and reading. TBLH is the location where the high order byte of the table data is stored after a

table read data instruction has been executed. Note that the lower order table data byte is transferred to

a user defined location.

StatusRegister

- 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). These arithmetic/logical operation

and system management flags are used to record the status and operation of the microcontroller.

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, operations related to the status register may give different results due to the different

instruction operations. The TO flag can be affected only by a system power-up, a WDT time-out or by

executing the

²CLR WDT² or ²HALT² instruction. The PDF flag is affected only by executing the

²HALT² or ²CLR WDT² instruction or during a system power-up.

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

· C is set if an 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.

· AC is set if an 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 logical operation is zero; otherwise Z is cleared.

· OV is set if an 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.

HT68F13/HT68F14/HT68F15

EnhancedI/OFlashType MCU

Rev.1.10

February9,2011

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