HT82K94A datasheet(9/43 Pages) HOLTEK

9 / 43 page

HT82K94E/HT82K94A

Rev. 1.50

October 11, 2007

Indirect Addressing Register

Location 00H and 02H are indirect addressing registers

that are not physically implemented. Any read/write op-

eration of [00H] ([02H]) will access data memory pointed

to by MP0 (MP1). Reading location 00H (02H) itself indi-

rectly will return the result 00H. Writing indirectly results

in no operation.

The indirect addressing pointer (MP0) always point to

Bank0 RAM addresses regardless of the value of the

Bank Register (BP).

The indirect addressing pointer (MP1) can access

Bank0 or Bank1 RAM data according to the value of BP

which is set to

²0² or ²1² respectively.

The memory pointer registers (MP0 and MP1) are 8-bit

registers.

Accumulator

The accumulator is closely related to ALU operations. It

is also mapped to location 05H 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 (0AH) 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 operation 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

tion operations related to the status register may give

different results from those intended.

The TO flag can be affected only by system power-up, a

WDT time-out or executing the

²CLR WDT² or ²HALT²

instruction. The PDF flag can be affected only by ex-

ecuting the

²HALT² or ²CLR WDT² instruction or dur-

ing 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.

Interrupt

The device provides internal timer/event counter and

USB interrupts. The Interrupt Control Register

(INTC;0BH) contains the interrupt control bits to set the

enable/disable and the interrupt request flags.

Once an interrupt subroutine is serviced, all the other in-

terrupts will be blocked (by clearing the EMI bit). This

scheme may prevent any further interrupt nesting. Other

interrupt requests may occur during this interval but only

Bit No.

Label

Function

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.

1AC

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 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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