HT46RB50 Holtek Semiconductor, HT46RB50 Datasheet - Page 8

• Manufacturer Part Number: HT46RB50
• Description: A/D Type USB 8-Bit MCU
• Manufacturer: Holtek Semiconductor

At a subroutine call or an interrupt acknowledgment, the
contents of the program counter are pushed onto the
stack. At the end of the subroutine or an interrupt rou-
tine, signaled by a return instruction (RET or RETI), 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 will be recorded but the
acknowledgment will be inhibited. When the stack
pointer is decremented (by RET or RETI), the interrupt is
serviced. This feature prevents stack overflow, allowing
the programmer to use the structure more easily. If the
stack is full and a CALL is subsequently executed,
stack overflow occurs and the first entry will be lost (only
the most recent 6 return addresses are stored).
Data Memory - RAM
The data memory (RAM) is designed with 238 8 bits,
and is divided into two functional groups, namely; spe-
cial function registers (46 8 bits) and general purpose
data memory (192 8 bits) most of which are read-
able/writeable, although some are read only.
The remaining space before 40H is reserved for future
expanded 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 memory areas can handle arithmetic,
logic, increment, decrement and rotate operations di-
rectly. Except for some dedicated bits, each bit in the
data memory can be set and reset by SET [m].i and
memory pointer registers (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. 1.10
00H . The general purpose data memory, addressed
CLR [m].i . They are also indirectly accessible through
8
RAM Mapping
September 7, 2006
HT46RB50