HT48R063/064/065/066/0662/067
Memory will always result in Bank 0 being accessed irre-
spective of the value of the Bank Pointer.
the status registers are important and if the interrupt rou-
tine 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 - 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.
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 con-
trol 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 in-
itialisation, it is important to first setup the control regis-
ters 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 spe-
cific bits of the I/O control registers during normal pro-
gram operation is a useful feature of these devices.
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.
In addition, on entering an interrupt sequence or execut-
ing a subroutine call, the status register will not be
pushed onto the stack automatically. If the contents of
·
STATUS Register
Bit
7
6
5
TO
R
4
PDF
R
3
OV
R/W
x
2
Z
1
AC
R/W
x
0
Name
R/W
C
¾
¾
¾
¾
¾
¾
R/W
x
R/W
x
POR
0
0
²x² unknown
Bit 7, 6
Unimplemented, read as ²0²
TO: Watchdog Time-Out flag
Bit 5
Bit 4
Bit 3
0: After power up or executing the ²CLR WDT² or ²HALT² instruction
1: A watchdog time-out occurred.
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.
Rev. 1.10
21
June 9, 2009
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
