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 ma
-
nipulating specific bits of the I/O control registers during normal program operation is a useful fea
-
ture of these devices.
UART Registers - USR, UCR1, UCR2, TXR/RXR, BRG
The HT48RU80/HT48CU80 devices each contain an internal UART function which is controlled
via these five registers. The USR is the status register for the UART while UCR1 and UCR2 are
the two control registers. The actual data that is to be transmitted or that is received on the serial in
-
terface is stored in the TXR/RXR register while the Baud Rate for the UART is setup via the BRG
register.
Input/Output Ports
Holtek microcontrollers offer considerable flexibility on their I/O ports. With the input or output des
-
ignation of every pin fully under user program control, pull-high options for all pins and wake-up op
-
tions on certain pins, the user is provided with an I/O structure to meet the needs of a wide range of
application possibilities.
Depending upon which device or package is chosen, the microcontroller range provides from 21
to 56 bidirectional input/output lines labeled with port names PA, PB, PC, etc. These I/O ports are
mapped to the Data Memory with specific addresses as shown in the Special Purpose Data Mem
-
ory table. All of these I/O ports can be used for input and output operations. For input operation,
these ports are non-latching, which means the inputs must be ready at the T2 rising edge of in
-
struction ²MOV A,[m]², 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 external resistor. To eliminate the need for these external resistors, all I/O pins, when con-
figured as an input have the capability of being connected to an internal pull-high resistor. These
pull-high resistors are selectable via configuration options and are implemented using a weak
PMOS transistor. Note that if the pull-high option is selected, then all I/O pins on that port will be
connected to pull-high resistors, individual pins cannot be selected for pull-high resistor options.
Port A Wake-up
Each device has a HALT feature enabling the microcontroller to enter a Power Down Mode and
preserve power, a feature that is important 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 A pins from high to low. After a ²HALT² instruction forces the microcontroller into enter
-
ing a HALT condition, the processor will remain idle or in a low-power state until the logic condition
of the selected wake-up pin on Port A changes from high to low. This function is especially suitable
for applications that can be woken up via external switches. Note that each pin on Port A can be se
-
lected individually to have this wake-up feature.
36
I/O Type MCU
To Next Page
Loading...
Need help?
General
