HT46R064D/065D/066D
Enhanced A/D Type 8-Bit OTP MCU with LED Driver
The Z, OV, AC and C flags generally reflect the status of the latest operations.
In addition, on entering an interrupt sequence or executing a subroutine call, the status register will not
be pushed onto the stack automatically. If the contents of the status registers are important and if the
interrupt routine can change the status register, precautions must be taken to correctly save it. Note that
bits 0~3 of the STATUS register are both readable and writeable bits.
STATUS Register
Bit
Name
R/W
7
6
5
TO
R
4
PDF
R
3
OV
R/W
x
2
Z
1
AC
R/W
x
0
C
¾
¾
¾
¾
¾
¾
R/W
x
R/W
x
POR
0
0
²x² unknown
Bit 7, 6
Bit 5
unimplemented, read as ²0²
TO: Watchdog Time-Out flag
0: After power up or executing the ²CLR WDT² or ²HALT² instruction
1: A watchdog time-out occurred.
Bit 4
Bit 3
PDF: Power down flag
0: After power up or executing the ²CLR WDT² instruction
1: By executing the ²HALT² instruction
OV: Overflow flag
0: no overflow
1: an operation results in a carry into the highest-order bit but not a carry out of the
highest-order bit or vice versa.
Bit 2
Bit 1
Z: Zero flag
0: The result of an arithmetic or logical operation is not zero
1: The result of an arithmetic or logical operation is zero
AC: Auxiliary flag
0: no auxiliary carry
1: 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
Bit 0
C: Carry flag
0: no carry-out
1: an operation results in a carry during an addition operation or if a borrow does not take place
during a subtraction operation
C is also affected by a rotate through carry instruction.
Input/Output Ports and Control Registers
Within the area of Special Function Registers, the port PA, PB, etc data I/O registers and their
associated control register PAC, PBC, etc play a prominent role. These registers are mapped to specific
addresses within the Data Memory as shown in the Data Memory table. The data I/O registers, are
used to transfer the appropriate output or input data on the port. The control registers specifies which
pins of the port are set as inputs and which are set as outputs. To setup a pin as an input, the
corresponding bit of the control register must be set high, for an output it must be set low. During
program initialisation, it is important to first setup the control registers to specify which pins are
outputs and which are inputs before reading data from or writing data to the I/O ports. One flexible
feature of these registers is the ability to directly program single bits using the ²SET [m].i² and ²CLR
[m].i² instructions. The ability to change I/O pins from output to input and vice versa by manipulating
specific bits of the I/O control registers during normal program operation is a useful feature of these
devices.
Rev. 1.00
23
January 12, 2011
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
