HT46R232/HT46C232
Indirect Addressing Register
information and controls the operation sequence. Ex-
cept for the TO and PDF flags, bits in the status register
can be altered by instructions similar to other registers.
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 in-
tended. The TO and PDF flags can only be changed by
a Watchdog Timer overflow, chip power-up, or clearing
the Watchdog Timer and executing the ²HALT² instruc-
tion.
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. 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.
The Z, OV, AC, and C flags reflect the status of the latest
operations. On entering the interrupt sequence or exe-
cuting the subroutine call, the status register will not be
automatically 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.
Accumulator - ACC
The accumulator is closely related to ALU operations. It
is also mapped to location 05H of the RAM and capable
of operating with immediate data. The data movement
between two data memory locations must pass through
the accumulator.
Interrupts
The device provides an external interrupt, two internal
timer/event counter interrupt, the A/D converter interrupt
and the I2C Bus interrupts. The interrupt control register
0 (INTC0;0BH) and interrupt control register 1
(INTC1;1EH) contains the interrupt control bits to set the
enable/disable and the interrupt request flags.
Arithmetic and Logic Unit - ALU
This circuit performs 8-bit arithmetic and logic operations.
The ALU provides the following functions:
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Arithmetic operations (ADD, ADC, SUB, SBC, DAA)
Logic operations (AND, OR, XOR, CPL)
Rotation (RL, RR, RLC, RRC)
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 INTC0 and INTC1
may be set to allow interrupt nesting. If the stack is full,
the interrupt request will not be acknowledged, even if the
related interrupt is enabled, until the SP is decremented.
If immediate service is desired, the stack must be pre-
vented from becoming full.
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
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
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 ro-
tate through carry instruction.
0
C
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.
1
2
3
AC
Z
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 system power-up or executing the ²CLR WDT² instruction. PDF is set by
executing the ²HALT² instruction.
4
PDF
TO is cleared by system power-up or executing the ²CLR WDT² or ²HALT² instruction. TO is
set by a WDT time-out.
5
TO
6, 7
¾
Unused bit, read as ²0²
Status (0AH) Register
Rev. 1.50
9
January 21, 2009
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
