Rev. 1.00
36
September 11, 2018
Rev. 1.00
37
September 11, 2018
HT45F4050
A/D NFC Flash MCU
HT45F4050
A/D NFC Flash MCU
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 programmers by locating it within the Special Purpose area of the Data Memory. By
manipulating this register, direct jumps to other program locations are easily implemented. Loading
a value directly into this PCL register will cause a jump to the specified Program Memory location,
however, as the register is only 8-bit wide, only jumps within the current Program Memory page are
permitted. When such operations are used, note that a dummy cycle will be inserted.
Look-up Table Registers – TBLP, TBHP, TBLH
These three special function registers are used to control operation of the look-up table which is
stored in the Program Memory. TBLP and TBHP are the table pointers and indicate the location
where the table data is located. Their value must be setup before any table read commands are
executed. Their value can be changed, for example using the "INC" or "DEC" 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 defined location.
Status Register – STATUS
This 8-bit register contains the zero flag (Z), carry flag (C), auxiliary carry flag (AC), overflow flag
(OV), SC flag, CZ flag, power down flag (PDF), and watchdog time-out flag (TO). These arithmetic/
logical operation and system management 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, operations related to the status register may give different results 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 "CLR WDT" or "HALT" instruction. The PDF flag is affected only by
executing the "HALT" or "CLR WDT" instruction or during a system power-up.
The Z, OV, AC, C SC and CZ flags generally reflect the status of the latest operations.
•
C is set if an 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.
•
AC is set if an 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.
•
Z is set if the result of an arithmetic or logical operation is zero; otherwise Z is cleared.
•
OV is set if an 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.
