HT46R74D-1 Holtek Semiconductor, HT46R74D-1 Datasheet - Page 9

• Manufacturer Part Number: HT46R74D-1
• Description: Dual Slope A/D Type MCU
• Manufacturer: Holtek Semiconductor

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ment, the contents of the program counter is pushed
onto the stack. At the end of the subroutine or interrupt
routine, indicated by a return instruction, RET or RETI,
the contents of the program counter is restored to its
previous value from the stack. After a chip reset, the SP
will point to the top of the stack.
If the stack is full and a non-masked interrupt takes
place, the interrupt request flag is recorded but the ac-
knowledgment is still inhibited. Once the SP is decre-
mented, using a RET or RETI instruction, the interrupt is
serviced. This feature prevents a stack overflow, allow-
ing the programmer to use the structure easily. Like-
wise, if the stack is full, and a CALL is subsequently
executed, a stack overflow occurs and the first entry is
lost as only the most recent 6 return addresses are
stored.
Data Memory - RAM
Bank 0 of the data memory has a capacity of 123 8 bits,
and is divided into two functional groups, namely the
special function registers, which have a 27 8 bit
capacity and the general purpose data memory which
have a 96 8 bit capacity. Most locations are read-
able/writable, although some are read only. The special
function register are overlapped in all banks.
Any unused locations before 20H will return a zero re-
sult if read. The general purpose data memory, ad-
dressed from 20H to 7FH , is used for data and control
information under instruction commands. All of the data
memory 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 the SET [m].i and CLR [m].i
instructions. They are also indirectly accessible through
the memory pointer registers, MP0 and MP1.
Bank 1 contains the LCD Data Memory locations. After
first setting up the Bank Pointer, BP, to the value of
cessed indirectly using Memory Pointer MP1. With BP
set to a value of 01H , using MP1 to indirectly read or
write to the data memory areas with addresses from
40H~4FH will result in operations to Bank 1. Directly ad-
dressing the Data Memory will always result in Bank 0
being accessed irrespective of the value of BP.
Indirect Addressing Register
Locations 00H and 02H are indirect addressing regis-
ters that are not physically implemented. Any read/write
operations on [00H] and [02H] accesses the RAM
locations pointed to by MP0 and MP1 respectively.
Reading locations 00H or 02H indirectly returns the re-
sult 00H. Writing to them 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 7-bit registers and
Rev. 1.10
01H to access Bank 1, this bank must then be ac-
9
are used to access the Data Memory in combination
with the indirect addressing registers. MP0 can only be
used with the data memory, while MP1 can be used with
both the data memory and the LCD display memory.
Accumulator - ACC
The accumulator, ACC, is related to the ALU operations.
It is 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
This circuit performs 8-bit arithmetic and logic opera-
tions and provides the following functions:
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.)
RAM Mapping
HT46R74D-1
January 11, 2007