HT46R64/HT46C64
The ALU not only saves the results of a data operation
but also changes the status register.
[m].i². They are also indirectly accessible through mem-
ory pointer registers (MP0;01H/MP1;03H). The space
before 40H is overlapping in each bank.
Status Register - STATUS
Indirect Addressing Register
The status register (0AH) is 8 bits wide and contains, a
carry flag (C), an auxiliary carry flag (AC), a zero flag (Z),
an overflow flag (OV), a power down flag (PDF), and a
watchdog time-out flag (TO). It also records the status
information and controls the operation sequence.
Location 00H and 02H are indirect addressing registers
that are not physically implemented. Any read/write op-
eration of [00H] and [02H] accesses the RAM pointed to
by MP0 (01H) and MP1(03H) respectively. Reading lo-
cation 00H or 02H indirectly returns the result 00H.
While, writing it indirectly leads to no operation.
Except for the TO and PDF flags, bits in the status regis-
ter can be altered by instructions similar to other regis-
ters. Data written into the status register does not alter
the TO or PDF flags. Operations related to the status
register, however, may yield different results from those
intended. The TO and PDF flags can only be changed
by a Watchdog Timer overflow, chip power-up, or clear-
ing the Watchdog Timer and executing the ²HALT² in-
struction. The Z, OV, AC, and C flags reflect the status of
the latest operations.
The function of data movement between two indirect ad-
dressing registers is not supported. The memory pointer
registers, MP0 and MP1, are both 8-bit registers used to
access the RAM by combining corresponding indirect
addressing registers. MP0 can only be applied to data
memory, while MP1 can be applied to data memory and
LCD display memory.
Accumulator - ACC
On entering the interrupt sequence or executing the
subroutine call, the status register will not be automati-
cally pushed onto the stack. If the contents of the status
is important, and if the subroutine is likely to corrupt the
status register, the programmer should take precautions
and save it properly.
The accumulator (ACC) is related to the ALU opera-
tions. It is also mapped to location 05H of the RAM and
is capable of operating with immediate data. The data
movement between two data memory locations must
pass through the ACC.
Arithmetic and Logic Unit - ALU
Interrupts
This circuit performs 8-bit arithmetic and logic opera-
tions and provides the following functions:
The device provides two external interrupts, two internal
timer/event counter interrupts, an internal time base in-
terrupt, and an internal real time clock interrupt and the
A/D converter interrupt (NMI). The interrupt control reg-
ister 0 (INTC0;0BH) and interrupt control register 1
(INTC1;1EH) both contain the interrupt control bits that
are used to set the enable/disable status and interrupt
request flags.
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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 etc.)
Labels
Bits
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.
C
0
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.
AC
Z
1
2
3
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.
OV
PDF is cleared by either a system power-up or executing the ²CLR WDT² instruction. PDF is
set by executing the ²HALT² instruction.
PDF
4
TO is cleared by a system power-up or executing the ²CLR WDT² or ²HALT² instruction. TO is
set by a WDT time-out.
TO
5
6~7
¾
Unused bit, read as ²0²
Status Register
Rev. 1.40
10
September 21, 2004
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
