Special Vectors
Within the Program Memory, certain locations are reserved for special usage such as reset and in
-
terrupts.
·
Location 000H
This vector is reserved for use by the chip reset for program initialization. After a chip reset is ini
-
tiated, the program will jump to this location and begin execution.
·
Location 004H
This vector is used by the external interrupt. If the external interrupt pin on the device goes low,
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 internal vector is used by the Timer/Event Counter. If a counter overflow occurs, the pro
-
gram will jump to this location and begin execution if the timer interrupt is enabled and the stack
is not full. For the HT46R24/HT46C24 devices, which has dual timers, this timer is known as
Timer/Event Counter 0 or TMR0, for the other devices the timer is known as TMR.
·
Location 00CH
With the exception of the HT46R24/HT46C24 devices, this internal vector is used by the A/D
converter. When an A/D conversion cycle is complete, the program will jump to this location and
begin execution if the A/D interrupt is enabled and the stack is not full. For the
HT46R24/HT46C24 devices, this internal vector is used by its Timer/Event Counter 1. If a TMR1
counter overflow occurs, the program will jump to this location and begin execution if the internal
interrupt is enabled and the stack is not full.
·
Location 010H
With the exception of the HT46R47/HT46C47 and HT46R24/HT46C24 devices, this internal
vector is used by the I
2
C bus interface. When the I
2
C bus requires data transfer, the program will
jump to this location and begin execution if the I
2
C interrupt is enabled and the stack is not full.
For the HT46R24/HT46C24 devices this internal vector is used by its A/D converter interrupt.
When the A/D conversion cycle in the HT46R24/HT46C24 is complete, the program will jump to
this location and begin execution if the A/D interrupt is enabled and the stack is not full.
· Location 014H
This vector, only available for the HT46R24/HT46C24 devices, is used by its I
2
C bus interface.
When the I
2
C bus of the HT46R24/HT46C24 requires data transfer, the program will jump to this
location and begin execution if the I
2
C interrupt is enabled and the stack is not full.
Look-up Table
Any location within the Program Memory can be defined as a look-up table where programmers
can store fixed data. To use the look-up table, the table pointer must first be setup by placing the
lower-order address of the look-up data to be retrieved in the Table Pointer Register TBLP. This
register defines the lower 8-bit address of the look-up table. After setting up the table pointer, the
table data can be retrieved from the current Program Memory page or last Program Memory page
using the ²TABRDC [m]² or ²TABRDL [m]² instructions respectively. When these instructions are
executed, the lower order table byte from the Program Memory will be transferred to the user de
-
fined Data Memory register [m] as specified in the instruction. The higher order table data byte
from the Program Memory will be transferred to the TBLH special register. Any unused bits in this
transferred higher order byte will be read as ²0².
20
A/D Type MCU
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