ht82a523r Holtek Semiconductor Inc., ht82a523r Datasheet - Page 9

• Manufacturer Part Number: ht82a523r
• Description: Ht82a523r -- Usb 2.0 Full Speed 8-bit Otp Mcu
• Manufacturer: Holtek Semiconductor Inc.

and is divided into two functional groups, namely; spe-
cial function registers (43 8 bits) and general purpose
data memory (192 8 bits) most of which are read-
able/writeable, although some are read only.
The unused space before 40H is reserved for future ex-
panded usage and reading these locations will get
from 40H to FFH, is used for data and control informa-
tion under instruction commands. All of the data mem-
ory areas can handle arithmetic, logic, increment,
decrement and rotate operations directly. Except for
some dedicated bits, each bit in the data memory can be
set and reset by SET [m].i and CLR [m].i . They are
also indirectly accessible through memory pointer regis-
ters (MP0;01H/MP1;03H).
Indirect Addressing Register
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 into 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.
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.
Rev. 1.30
00H . The general purpose data memory, addressed
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 ro-
tate 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
Arithmetic and Logic Unit - ALU
This circuit performs 8-bit arithmetic and logic operations.
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
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 in-
formation and controls the operation sequence. Except
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, how-
ever, 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 clearing the Watchdog
Timer and executing the HALT instruction.
The Z, OV, AC, and C flags reflect the status of the latest
operations. 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 is important, and if the subroutine is likely to
corrupt the status register, the programmer should take
precautions and save it properly.
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.)
Function
HT82A523R
May 13, 2008