ht82k94e Holtek Semiconductor Inc., ht82k94e Datasheet - Page 9

• Manufacturer Part Number: ht82k94e
• Description: Ht82k94e/ht82k94a -- Usb Multimedia Keyboard Encoder 8-bit Mcu
• Manufacturer: Holtek Semiconductor Inc.

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 0 or 1 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:
The ALU not only saves the results of a data operation
but also changes the status register.
Rev. 1.90
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)
Bit No.
6~7
0
1
2
3
4
5
Label
PDF
OV
AC
TO
C
Z
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 logic operation is zero; otherwise Z is cleared.
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 is cleared by system power-up or executing the CLR WDT instruction. PDF is set by
executing the HALT instruction.
TO is cleared by system power-up or executing the CLR WDT or HALT instruction. TO is
set by a WDT time-out.
Unused bit, read as 0
Status (0AH) Register
9
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
register will not change the TO or PDF flag. In addi-
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 CLR WDT or HALT
instruction. The PDF flag can be affected only by ex-
ecuting the HALT or CLR WDT 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
Function
HT82K94E/HT82K94A
April 29, 2008