HT49CA1 View Datasheet(PDF) - Holtek Semiconductor
Part Name
Description
MFG CO.
'HT49CA1' PDF : 58 Pages View PDF
HT49RA1/HT49CA1
P ro g ra m C o u n te r
T o p o f S ta c k
S ta c k
P o in te r
B o tto m o f S ta c k
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
S ta c k L e v e l 4
P ro g ra m
M e m o ry
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.
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,
SUB, SUBM, SBC, SBCM, DAA
· 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
Program Memory
The Program Memory is the location where the user code
or program is stored. For microcontrollers, two types of
Program Memory are usually supplied. The first type is
the One-Time Programmable, OTP, memory where us-
ers can program their application code into the device.
Devices with OTP memory are denoted by having an ²R²
within their device name. By using the appropriate pro-
gramming tools, OTP devices offer users the flexibility to
freely develop their applications which may be useful
during debug or for products requiring frequent upgrades
or program changes. OTP devices are also applicable for
use in applications that require low or medium volume
000H
In itia lis a tio n
V e c to r
004H
E x te rn a l
In te rru p t 0 V e c to r
008H
E x te rn a l
In te rru p t 1 V e c to r
0 0 C H T im e r /E v e n t C o u n te r
0 In te rru p t V e c to r
0 1 0 H T im e r /E v e n t C o u n te r
1 In te rru p t V e c to r
014H
T im e B a s e
In te rru p t V e c to r
018H
R TC
In te rru p t V e c to r
300H
3FFH
400H
7FFH
800H
FFFH
1 5 b its
Program Memory Structure
production runs. The other type of memory is the mask
ROM memory, denoted by having a ²C² within the device
name. These devices offer the most cost effective solu-
tions for high volume products.
Structure
The Program Memory has a capacity of 4K by 15 bits.
The Program Memory is addressed by the Program
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
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
This vector is used by the external interrupt. If the ex-
ternal interrupt pin INT0 on the device receives an ac-
tive edge, the program will jump to this location and
begin execution if the external interrupt is enabled and
the stack is not full.
· Location 008H
This vector is used by the external interrupt. If the ex-
ternal interrupt pin INT1 on the device receives an ac-
tive edge, the program will jump to this location and
begin execution if the external interrupt is enabled and
the stack is not full.
Rev. 1.10
8
March 30, 2014
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