HT45FM03B データシートの表示（PDF） - Holtek Semiconductor
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HT45FM03B Datasheet PDF : 83 Pages
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HT45FM03B
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.
Look-up Table Registers - TBLP, TBLH
These two special function registers are used to control
operation of the look-up table which is stored in the Pro-
gram Memory. TBLP is the table pointer and indicates
the location where the table data is located. Its value
must be setup before any table read commands are ex-
ecuted. Its value can be changed, for example using the
²INC² or ²DEC² instructions, allowing for easy table data
pointing and reading. TBLH is the location where the
high order byte of the table data is stored after a table
read data instruction has been executed. Note that the
lower order table data byte is transferred to a user de-
fined location.
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-
tions related to the status register may give different re-
sults due to the different instruction operations. The TO
flag can be affected only by a system power-up, a WDT
time-out or by executing the ²CLR WDT² or ²HALT² in-
struction. The PDF flag is affected only by executing the
²HALT² or ²CLR WDT² instruction or during a system
power-up.
The Z, OV, AC and C flags generally reflect the status of
the latest operations.
· C is set if an operation results in a carry during an ad-
dition operation or if a borrow does not take place dur-
ing a subtraction operation; otherwise C is cleared. C
is also affected by a rotate through carry instruction.
· AC is set if an operation results in a carry out of the
low nibbles in addition, or no borrow from the high nib-
ble into the low nibble in subtraction; otherwise AC is
cleared.
b7
b0
T O P D F O V Z A C C S T A T U S R e g is te r
A r ith m e tic /L o g ic O
C a r r y fla g
A u x ilia r y c a r r y fla g
Z e r o fla g
O v e r flo w fla g
p e r a tio n
F la g s
S y s te m M a n a g e m e n t F la g s
P o w e r d o w n fla g
W a tc h d o g tim e - o u t fla g
N o t im p le m e n te d , r e a d a s " 0 "
Status Register
Rev. 1.10
17
May 7, 2010
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