HT46F46E/HT46F47E/HT46F48E/HT46F49E
Stack
This is a special part of the memory which is used to
save the contents of the Program Counter only. The
stack can have either 4 or 6 levels depending upon
which device is selected and is neither part of the data
nor part of the program space, and is neither readable
nor writable. The activated level is indexed by the Stack
Pointer, SP, and is neither readable nor writable. At a
subroutine call or interrupt acknowledge signal, the con-
tents of the Program Counter are pushed onto the stack.
At the end of a subroutine or an interrupt routine, sig-
naled by a return instruction, RET or RETI, the Program
Counter is restored to its previous value from the stack.
After a device reset, the Stack Pointer will point to the
top of the stack.
P ro g ra m
C o u n te r
·
Logic operations: AND, OR, XOR, ANDM, ORM,
XORM, CPL, CPLA
·
Rotation RRA, RR, RRCA, RRC, RLA, RL, RLCA,
RLC
·
Increment and Decrement INCA, INC, DECA, DEC
·
Branch decision, JMP, SZ, SZA, SNZ, SIZ, SDZ,
SIZA, SDZA, CALL, RET, RETI
Flash Program Memory
The Program Memory is the location where the user
code or program is stored. For this device the Program
Memory is a Flash type, which means it can be pro-
grammed and reprogrammed a large number of times,
allowing the user the convenience of multiple code mod-
ifications on the same device. By using the appropriate
programming tools, this Flash memory device offer us-
ers the flexibility to conveniently debug and develop
their applications while also offering a means of field
programming.
Structure
The Program Memory has a capacity of 1K by 14, 2K by
14 or 4K by 15 bits depending upon which device is se-
lected. The Program Memory is addressed by the Pro-
gram Counter and also contains data, table information
and interrupt entries. Table data, which can be setup in
any location within the Program Memory, is addressed
by separate table pointer registers.
Special Vectors
Within the Program Memory, certain locations are re-
served for special usage such as reset and interrupts.
·
Location 000H
T o p o f S ta c k
S ta c k
P o in te r
S ta c k L e v e l 1
S ta c k L e v e l 2
S ta c k L e v e l 3
P ro g ra m
M e m o ry
B o tto m
o f S ta c k
S ta c k L e v e l N
If the stack is full and an enabled interrupt takes place,
the interrupt request flag will be recorded but the ac-
knowledge signal will be inhibited. When the Stack
Pointer is decremented, by RET or RETI, the interrupt
will be serviced. This feature prevents stack overflow al-
lowing the programmer to use the structure more easily.
However, when the stack is full, a CALL subroutine in-
struction can still be executed which will result in a stack
overflow. Precautions should be taken to avoid such
cases which might cause unpredictable program
branching.
Note:
For the HT46F46E, 4 levels of stack are avail-
able and for the HT46F47E,HT46F48E and
HT46F49E, 6 levels of stack are available.
This vector is reserved for use by the device reset for
program initialisation. After a device reset is initiated, the
program will jump to this location and begin execution.
·
Location 004H
Arithmetic and Logic Unit
-
ALU
The arithmetic-logic unit or ALU is a critical area of the
microcontroller that carries out arithmetic and logic op-
erations of the instruction set. Connected to the main
microcontroller data bus, the ALU receives related in-
struction codes and performs the required arithmetic or
logical operations after which the result will be placed in
the specified register. As these ALU calculation or oper-
ations may result in carry, borrow or other status
changes, the status register will be correspondingly up-
dated to reflect these changes. The ALU supports the
following functions:
·
Arithmetic operations: ADD, ADDM, ADC, ADCM,
This vector is used by the external interrupt. If the ex-
ternal interrupt pin on the device goes low, the pro-
gram will jump to this location and begin execution if
the external interrupt is enabled and the stack is not
full.
·
Location 008H
This internal vector is used by the Timer/Event Coun-
ter. If a counter overflow occurs, the program will jump
to this location and begin execution if the timer/event
counter interrupt is enabled and the stack is not full.
·
Location 00CH
This internal vector is used by the A/D converter.
When an A/D conversion cycle is complete, the pro-
gram will jump to this location and begin execution if
the A/D interrupt is enabled and the stack is not full.
SUB, SUBM, SBC, SBCM, DAA
Rev. 1.40
11
July 28, 2009
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
