HT45R06 Holtek Semiconductor, HT45R06 Datasheet - Page 9

• Manufacturer Part Number: HT45R06
• Description: A/D Type 8-Bit OTP MCU
• Manufacturer: Holtek Semiconductor

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.
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 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 CLR WDT or HALT instruction. The PDF flag
can be affected only by executing the HALT or CLR
WDT instruction or a system power-up.
Rev. 1.00
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
AC
OV
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 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.
PDF is cleared by a system power-up or executing the CLR WDT instruction. PDF is set
by executing the HALT instruction.
TO is cleared by a 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
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 a subroutine call, the status register will not be
automatically pushed onto the stack. 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 microcontroller provides external interrupts, an in-
ternal timer/event counter overflow interrupt, and an A/D
converter end-of-conversion interrupt. The interrupt
control registers (INTC;0BH ) contains the interrupt con-
trol bits to set the enable/disable and the interrupt re-
quest 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
the interrupt request flag is recorded. If a certain inter-
rupt requires servicing within the service routine, the
EMI bit and the corresponding bit of the INTC may be
set to allow interrupt nesting. If the stack is full, the inter-
rupt request will not be acknowledged, even if the re-
lated interrupt is enabled, until the SP is decremented. If
immediate service is desired, the stack must be pre-
vented from becoming full.
All these kinds of interrupts have a wake-up capability.
As an interrupt is serviced, a control transfer occurs by
pushing the program counter onto the stack, followed by
a branch to a subroutine at specified location in the pro-
gram memory. Only the program counter is pushed onto
the stack. If the contents of the register or status register
(STATUS) are altered by the interrupt service program
which corrupts the desired control sequence, the con-
tents should be saved in advance.
Function
HT45R06
May 24, 2005