HT45R35
·
·
·
Rotation - RL, RR, RLC, RRC
Bank Pointer - BP
Increment and Decrement - INC, DEC
When using instructions to access the general purpose
data memory in Bank 0 or Bank 1, it is necessary to en-
sure that the correct area is selected. The general pur-
pose data memory is sub-divided into two banks, Bank 0
and Bank 1 for this device. Selecting the correct data
memory area is achieved by using the bank pointer. If
data in Bank 0 or Bank 1 is to be accessed, the BP must
be set to the values ²00H² or ²01H² respectively, how-
ever, it must be noted that data in Bank 1 can only be ad-
dressed indirectly using the MP1 memory pointer and
the IAR1 indirect addressing register.
Branch decision - SZ, SNZ, SIZ, SDZ ....
The ALU not only saves the results of a data operation
but also changes the status register.
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). It
also records the status information and controls the op-
eration sequence.
Any direct addressing or any indirect addressing using
MP0 and IAR0 will always result in data from Bank 0 be-
ing accessed. The data memory is initialized 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 unchanged.
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 from those intended. The TO flag can be affected
only by a system power-up, a WDT time-out or execut-
ing the ²CLR WDT² or ²HALT² instruction.
It should be noted that the special function data memory
is not affected by the bank selection, which means that
the special function registers can be accessed from
within either Bank 0 or Bank 1.
The PDF flag can be affected only by executing a
²HALT² or ²CLR WDT² instruction or a system
power-up.
Accumulator
The accumulator is closely related to ALU operations. It
is also mapped to location ²05H² of the data memory
and can carry out immediate data operations. The data
movement between two data memory locations must
pass through the accumulator.
The Z, OV, AC and C flags generally reflect the status of
the latest operations.
In addition, on entering the interrupt sequence or exe-
cuting the subroutine call, the status register will not be
pushed onto the stack automatically. If the contents of
the status are important and if the subroutine can cor-
rupt the status register, precautions must be taken to
save it properly.
Arithmetic and Logic Unit - ALU
This circuit performs 8-bit arithmetic and logic opera-
tions. The ALU provides the following functions:
·
Arithmetic operations - ADD, ADC, SUB, SBC, DAA
·
Logic operations - AND, OR, XOR, CPL
Bit No.
Label
Function
C is set if the operation results in a carry during an addition operation or if a borrow does not
take place during a subtraction operation; otherwise C is cleared. C is also affected by a rotate
through carry instruction.
0
C
AC is set if the operation results in a carry out of the low nibbles in addition or no borrow from
the high nibble into the low nibble in subtraction; otherwise AC is cleared.
1
2
3
AC
Z
Z is set if the result of an arithmetic or logic operation is zero; otherwise Z is cleared.
OV is set if the operation results in a carry into the highest-order bit but not a carry out of the
highest-order bit, or vice versa; otherwise OV is cleared.
OV
PDF is cleared by system power-up or executing the ²CLR WDT² instruction.
PDF is set by executing the ²HALT² instruction.
4
PDF
TO is cleared by system power-up or executing the ²CLR WDT² or ²HALT² instruction.
5
TO
TO is set by a WDT time-out.
6~7
¾
Unused bit, read as ²0²
Status (0AH) Register
Rev. 1.30
9
May 14, 2010
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
