HT46R49 Holtek Semiconductor, HT46R49 Datasheet - Page 20

• Manufacturer Part Number: HT46R49
• Description: Cost-Effective A/D Type 8-Bit MCU
• Manufacturer: Holtek Semiconductor

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I/O Pin Structures
The following 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 initialization. After a reset, all of the I/O data
and port control registers 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 port
control registers, PAC, PBC, PCC and PDC, are then
programmed to setup some pins as outputs, these out-
put pins will have an initial high output value unless the
associated port data registers, PA, PB, PC and PD, are
first programmed. Selecting which pins are inputs and
which are outputs can be achieved byte-wide by loading
the correct values into the appropriate port control regis-
ter or by programming individual bits in the port control
register using the SET [m].i and CLR [m].i instruc-
tions. Note that when using these bit control instruc-
tions, a read-modify-write operation takes place. The
microcontroller must first read in the data on the entire
port, modify it to the required new bit values and then re-
write this data back to the output ports.
Port A has the additional capability of providing wake-up
functions. When the device is in the Power Down Mode,
various methods are available to wake the device up.
One of these is a high to low transition of any of the Port
A pins. Single or multiple pins on Port A can be setup to
have this function.
Note that some devices have different package types
which may result in some I/O pins not being bonded out.
Rev. 1.30
Read/Write Timing
8-bit Timer/Event Counter Structure
HT46R46/C46/R47/C47/R48A/C48A/R49
20
If these pins are setup as inputs they may oscillate and
increase power consumption, especially notable if the
device is in the Power Down Mode. It is therefore recom-
mended that any unbonded pins should be setup as out-
puts, or if setup as inputs, then they should be
connected to pull-high resistors.
Timer/Event Counters
The provision of timers form an important part of any
microcontroller giving the designer a means of carrying
out time related functions. Each device contains an in-
ternal 8-bit count-up timer. With three operating modes,
the timers can be configured to operate as a general
timer, external event counter or as a pulse width mea-
surement device. The provision of an internal 8-stage
prescaler to the timer clock circuitry gives added range
to the timer.
There are two registers related to the Timer/Event
Counter, TMR and TMRC. The TMR register is the reg-
ister that contains the actual timing value. Writing to
TMR places an initial starting value in the Timer/Event
Counter preload register while reading TMR retrieves
the contents of the Timer/Event Counter. The TMRC
register is a Timer/Event Counter control register, which
defines the timer options, and determines how the timer
is to be used. The timer clock source can be configured
to come from the internal system clock source or from
an external clock on shared pin PA4/TMR.
Configuring the Timer/Event Counter Input Clock
Source
The internal timer s clock source can originate from ei-
ther the system clock or from an external clock source.
The system clock input timer source is used when the
timer is in the timer mode or in the pulse width measure-
ment mode. The internal timer clock also passes
through a prescaler, the value of which is conditioned by
the bits PSC0, PSC1 and PSC2.
An external clock source is used when the timer is in the
event counting mode, the clock source being provided
on pin-shared pin PA4/TMR. Depending upon the condi-
tion of the TE bit, each high to low, or low to high transi-
tion on the PA4/TMR pin will increment the counter by
one.
June 5, 2008