ht82k73e Holtek Semiconductor Inc., ht82k73e Datasheet - Page 12

• Manufacturer Part Number: ht82k73e
• Description: 2.4ghz Keyboard Tx 8-bit Otp Mcu
• Manufacturer: Holtek Semiconductor Inc.

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
the status registers are important and if the interrupt rou-
tine can change the status register, precautions must be
taken to correctly save it.
Interrupt Control Registers - INTC
The microcontroller provides an internal timer/event
counter overflow interrupt. By setting various bits within
this register using standard bit manipulation instruc-
tions, the enable/disable function of each interrupt can
be independently controlled. A master interrupt bit within
this register, the EMI bit, acts like a global enable/dis-
able and is used to set all of the interrupt enable bits on
or off. This bit is cleared when an interrupt routine is en-
tered to disable further interrupt and is set by executing
the RETI instruction.
Timer/Event Counter Registers - TMRH, TMRL,
TMRC
All devices possess a single internal 16-bit count-up
timer. An associated register pair known as
TMRL/TMRH is the location where the timer 16-bit value
is located. This register can also be preloaded with fixed
data to allow different time intervals to be setup. An as-
sociated control register, known as TMRC, contains the
setup information for this timer, which determines in
what mode the timer is to be used as well as containing
the timer on/off control function.
Watchdog Timer Register - WDTS
The Watchdog function in 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.
Input/Output Ports and Control Registers
Within the area of Special Function Registers, the I/O
registers and and their associated control registers play
a prominent role. All I/O ports have a designated regis-
ter correspondingly labeled as PA, PB, PC, PD and
PE0~PE6. These labeled I/O registers are mapped to
specific addresses within the Data Memory as shown in
the Data Memory table, which are used to transfer the
appropriate output or input data on that port. With each
I/O port there is an associated control register labeled
Rev. 1.00
12
PAC, PBC, PCC, PDC and PEC0~PEC6, also mapped
to specific addresses with the Data Memory. The control
register specifies which pins of that 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 SET [m].i and
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.
Input/Output Ports
Holtek microcontrollers offer considerable flexibility on
their I/O ports. With the input or output designation of ev-
ery pin fully under user program control, pull-high op-
tions for all ports and wake-up options, the user is
provided with an I/O structure to meet the needs of a
wide range of application possibilities.
The microcontroller provides 39 bidirectional input/out-
put lines labeled with port names PA, PB, PC, PD and
PE0~PE6. These I/O ports are mapped to the Data
Memory with addresses as shown in the Special Pur-
pose Data Memory table. All of these I/O lines can be
used for input and output operations and one line as an
input only. For input operation, these ports are
non-latching, which means the inputs must be ready at
the T2 rising edge of instruction MOV A,[m] , where m
denotes the port address. For output operation, all the
data is latched and remains unchanged until the output
latch is rewritten.
Pull-high Resistors
Many product applications require pull-high resistors for
their switch inputs usually requiring the use of an exter-
nal resistor. To eliminate the need for these external re-
sistors, I/O pins, when configured as an input have the
capability of being connected to an internal pull-high re-
sistor. The pull-high resistors are selectable via configu-
ration options and are implemented using weak PMOS
transistors. Each pin on all of I/O can be selected indi-
vidually to have this pull-high Resistors feature and
each nibble on each of the other ports.
Port Pin Wake-up
If the HALT instruction is executed, the device will enter
the Power Down Mode, where the system clock will stop
resulting in power being conserved, a feature that is im-
portant for battery and other low-power applications.
Various methods exist to wake-up the microcontroller,
one of which is to change the logic condition on one of
the port pins from high to low. After a HALT instruction
CLR [m].i instructions. The ability to change I/O pins
HT82K73E
April 16, 2008