ht82k74e Holtek Semiconductor Inc., ht82k74e Datasheet - Page 19

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

output register. However, it should be noted that the pro-
gram will in fact only read the status of the output data
latch and not the actual logic status of the output pin.
Pin-shared Functions
The flexibility of the microcontroller range is greatly en-
hanced by the use of pins that have more than one func-
tion. Limited numbers of pins can force serious design
constraints on designers but by supplying pins with
multi-functions, many of these difficulties can be over-
come. The chosen function of the multi-function I/O pins
is set by application program control.
Rev. 1.00
External Timer Clock Input
The external timer pin TMR is pin-shared with the I/O
pin PA2. To configure this pin to operate as timer input,
the corresponding control bits in the timer control reg-
ister must be correctly set. For applications that do not
require an external timer input, this pin can be used as
a normal I/O pin. Note that if used as a normal I/O pin
the timer mode control bits in the timer control register
must select the timer mode, which has an internal
clock source, to prevent the input pin from interfering
with the timer operation.
The VA/VB is for V-axis Function
The VA/VB pins are shared with the pins PD0/PD1.
PD0 or PD1 have falling and rising edge wake-up func-
tions if their wake-up function is enabled by the related
configuration option. In the Power-down mode, if PD0
wakes up the MCU, the bit3 named VA_wake-up in the
Wake-up Status Register WSR will be set. Similarly, if
PD1 wakes up the MCU, bit4 named VB_wakeup in the
Wake-up Status Register WSR will be set. If the bit
VA_wake-up or VB_wakeup is read by application pro-
gram, the bit will be cleared.
The ZA/ZB is for Z-axis function
The ZA/ZB pins are shared with the PD2/PD3, PD2 or
Input/Output Ports
19
I/O Pin Structures
The diagrams illustrate the I/O pin internal structures. As
the exact logical construction of the I/O pin may differ
from these drawings, they are supplied as a guide only
to assist with the functional understanding of the I/O
pins.
Programming Considerations
Within the user program, one of the first things to con-
sider is port initialisation. After a reset, all of the data and
port control register will be set high. This means that all
I/O pins will default to an input state, the level of which
depends on the other connected circuitry and whether
pull-high options have been selected. If the PAC, PBC,
PCC, PDC and PEC port control registers are pro-
grammed to setup some pins as outputs, these output
pins will have an initial high output value unless the as-
sociated PA, PB, PC, PD and PE port data registers are
first programmed. Selecting which pins are inputs and
which are outputs can be achieved byte-wide by loading
PD3 has falling and rising edge wake-up function if its
wake-up function is enabled by related configuration
option. In halt mode if PD2 wakes up the MCU, the
bit6 named ZA_wakeup in the Wake-up Status Regis-
ter WSR will be set. Similarly, if PD3 wakes up the
MCU, the bit7 named ZB_wake-up in the Wake-up
Status Register WSR will be set. If the bit ZA_wake-up
or ZB_wakeup is read by application program, the bit
will be cleared.
Read/Write Timing
HT82K74E/HT82K74EE
December 15, 2009