ht82a836r Holtek Semiconductor Inc., ht82a836r Datasheet - Page 14

• Manufacturer Part Number: ht82a836r
• Description: Usb Audio Mcu
• Manufacturer: Holtek Semiconductor Inc.

Bank Pointer - BP
The Data Memory is divided into two Banks, known as
Bank 0 and Bank 1. Selecting the required Data Memory
area is achieved using the Bank Pointer. If data in Bank
0 is to be accessed, then the BP register must be loaded
with the value 00 , while if data in Bank 1 is to be ac-
cessed, then the BP register must be loaded with the
value 01 .
Using Memory Pointer MP0 and Indirect Addressing
Register IAR0 will always access data from Bank 0, irre-
spective of the value of the Bank Pointer.
The Data Memory is initialised to Bank 0 after a reset,
except for the WDT time-out reset in the Power Down
Mode, in which case, the Data Memory bank remains
unaffected. Directly addressing the Data Memory will al-
ways result in Bank 0 being accessed irrespective of the
value of the Bank Pointer.
Accumulator - ACC
The Accumulator is central to the operation of any
microcontroller and is closely related with operations
carried out by the ALU. The Accumulator is the place
where all intermediate results from the ALU are stored.
Without the Accumulator it would be necessary to write
the result of each calculation or logical operation such
as addition, subtraction, shift, etc., to the Data Memory
resulting in higher programming and timing overheads.
Data transfer operations usually involve the temporary
storage function of the Accumulator; for example, when
transferring data between one user defined register and
another, it is necessary to do this by passing the data
through the Accumulator as no direct transfer between
two registers is permitted.
Program Counter Low Register - PCL
To provide additional program control functions, the low
byte of the Program Counter is made accessible to pro-
grammers by locating it within the Special Purpose area
of the Data Memory. By manipulating this register, direct
jumps to other program locations are easily imple-
mented. Loading a value directly into this PCL register
will cause a jump to the specified Program Memory lo-
cation, however, as the register is only 8-bit wide, only
jumps within the current Program Memory page are per-
mitted. When such operations are used, note that a
dummy cycle will be inserted.
Rev. 1.00
Bank Pointer
14
Look-up Table Registers - TBLP, TBLH, TBHP
These three special function registers are used to con-
trol operation of the look-up table, which is stored in the
Program Memory. TBLP is the table low byte pointer and
indicates the lowest 8-bit address location where the ta-
ble data is located. TBHP is the table high byte pointer
and indicates the highest bit address location where the
table data is located. The TBHP high byte table pointer
can only be used if its configuration option is selected.
The table pointers must be setup before any table read
commands are executed. Their value can be changed,
for example using the INC or DEC instructions, al-
lowing for easy table data pointing and reading. If the
TBHP configuration is enabled, then the TBLP and
TBHP register pair can be used together with the
the program memory. TBLH is the location where the
higher order byte of the table data is stored after a table
read data instruction has been executed. The lower or-
der table data byte is transferred to a user defined loca-
tion.
Watchdog Timer Register - WDTS
The Watchdog feature of the microcontroller provides
an automatic reset function giving the microcontroller a
means of protection against spurious jumps to incorrect
Program Memory addresses. To implement this, a timer
is provided within the microcontroller which will issue a
reset command when its value overflows. To provide
variable Watchdog Timer reset times, the Watchdog
Timer clock source can be divided by various division ra-
tios, the value of which is set using the WDTS register.
By writing directly to this register, the appropriate divi-
sion ratio for the Watchdog Timer clock source can be
setup. Note that only the lower 3 bits are used to set divi-
sion ratios between 1 and 128.
Status Register - STATUS
This 8-bit register contains the zero flag (Z), carry flag
(C), auxiliary carry flag (AC), overflow flag (OV), power
down flag (PDF), and watchdog time-out flag (TO).
These arithmetic/logical operation and system manage-
ment flags are used to record the status and operation of
the microcontroller.
With the exception of the TO and PDF flags, bits in the
status register can be altered by instructions like most
other registers. Any data written into the status register
will not change the TO or PDF flag. In addition, opera-
TABRDC instruction to point directly to any location in
HT82A836R
March 20, 2008