HT45R35V Holtek Semiconductor Inc., HT45R35V Datasheet - Page 23

• Manufacturer Part Number: HT45R35V
• Description: C/r To F Type 8-bit Otp Mcu
• Manufacturer: Holtek Semiconductor Inc.

Input/Output Ports
There are 9 bidirectional input/output lines in the
microcontroller, all located within port PA and PB. All of
these I/O ports can be used for input and output opera-
tions. For input operation, these ports are non-latching,
that is, the inputs must be ready at the T2 rising edge of
the MOV A,[m] instruction. For output operation, all the
data is latched and remains unchanged until the output
latch is rewritten.
Each I/O line has its own control register, known as PAC
and PBC, to control the input/output configuration. With
this control register, the pin status is either a CMOS out-
put or a Schmitt trigger input, but can be reconfigured
dynamically, under software control. To function as an
input, the corresponding bit in the control register must
be written with a 1 . The input source also depends on
the control register. If the control register bit is 1 , the input
will read the pad state. If the control register bit is 0 , the
contents of the latches will move to the internal bus. The
latter is possible in the read-modify-write instruction.
When setup as an output the output types are CMOS.
After a device reset, the I/O ports will be initially all setup
as inputs, and will therefore be in a high state if the
configuration options have selected pull-high resistors,
otherwise they will be in a floating condition. Each bit of
these input/output latches can be set or cleared by the
Some instructions first input data and then follow the
output operations. For example, SET [m].i , CLR
[m].i , CPL [m] , CPLA [m] read the entire port states
into the CPU, execute the defined operations
(bit-operation), and then write the results back to the
latches or the accumulator.
Rev. 1.00
SET [m].i and CLR [m].i instructions.
Input/Output Ports
23
Each line of port A has the capability of waking-up the
device.
Each line of port A and port B has a pull-high option.
Once the pull-high option is selected, the I/O line will
have a pull-high resistor connected. Otherwise, the
pull-high resistors are absent. It should be noted that a
non-pull-high I/O line operating in an input mode will be
in a floating state.
The PA0, PA1 and PA2 are pin-shared with INT0, INT1
and TMR pins, respectively. Pins PA0~PA3 and
PA4~PA7 are pin-shared with RC1~RC4 and
RC9~RC12, respectively. If configuration options select
PA0~PA7 to be RC input pins, then the corresponding
bits in the PA data register and PA control register will be
unimplemented.
It is recommended that unused or not bonded out I/O
lines should be set as output pins using software in-
struction to avoid consuming power under input floating
state.
VFD Driver
The device includes a VFD driver function to drive VFD
panel high voltage filaments and buzzer. The
microcontroller communicates serially with the VFD
driver transmitting the display data into a 24-bit shift reg-
ister within the driver. This VFD driver converts the shift
register into VFD panel driving signals and makes the
necessary voltage level shifting. The microcontroller will
only transmit data to the VFD driver, no data is transmit-
ted from the VFD driver to the microcontroller.
January 15, 2009
HT45R35V