ht82k74e Holtek Semiconductor Inc., ht82k74e Datasheet - Page 18

• Manufacturer Part Number: ht82k74e
• Description: 27mhz Keyboard/ Mouse Tx 8-bit Mcu
• Manufacturer: Holtek Semiconductor Inc.

Data EEPROM Timing Diagrams
Note:
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 option for all I/O pins, the
user is provided with an I/O structure to meet the needs
of a wide range of application possibilities.
The device provides 36-bit bidirectional input/output
lines labeled with port names PA, PB, PC, PD and PE.
These I/O ports are mapped to the Data Memory with
addresses as shown in the Special Purpose Data Mem-
ory table. All of these I/O lines 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 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.
Port Pin Wake-up
If the HALT instruction is executed, the device will enter
the Power Down Mode, where the system clock will stop
Rev. 1.00
The write cycle time t
condition of sequential command.
WR
is the time from a valid stop condition of a write sequence to the end of the valid start
18
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 or low to high. After a
HALT instruction forces the microcontroller into the
Power Down Mode, the processor will remain in a
low-power state until the logic condition of the selected
wake-up pin on the port pin changes from high to low or
low to high. This function is especially suitable for appli-
cations that can be woken up via external switches.
Each pin on PA (by bit), PB, PC, PD, PE has the capabil-
ity to wake-up (by nibble) the device by falling and rising
edges. It means once there are one pin in is low or high
the I/O cannot wake-up the MCU.
I/O Port Control Registers
Each I/O port has its own control register PAC, PBC,
PCC, PDC and PEC to control the input/output configu-
ration. With this control register, each CMOS output or
input with or without pull-high resistor structures can be
reconfigured dynamically under software control. Each
of the I/O ports is directly mapped to a bit in its associ-
ated port control register.
For the I/O pin to function as an input, the corresponding
bit of the control register must be written as a 1 . This
will then allow the logic state of the input pin to be di-
rectly read by instructions. When the corresponding bit
of the control register is written as a 0 , the I/O pin will
be setup as a CMOS output. If the pin is currently setup
as an output, instructions can still be used to read the
HT82K74E/HT82K74EE
December 15, 2009