Tm Operation; Tm C�Ock So�Rce; Tm Interr�Pts; Tm Externa� Pins - Holtek HT68F Series Manual

TM Operation

The three different types of TM offer a diverse range of functions, from simple timing operations
to PWM signal generation. The key to understanding how the TM operates is to see it in terms of
a free running counter whose value is then compared with the value of pre-programmed internal
comparators. When the free running counter has the same value as the pre-programmed comparator,
known as a compare match situation, a TM interrupt signal will be generated which can clear the
counter and perhaps also change the condition of the TM output pin. The internal TM counter is
driven by a user selectable clock source, which can be an internal clock or an external pin.
TM Clock Source
The clock source which drives the main counter in each TM can originate from various sources.
The selection of the required clock source is implemented using the TnCK2~TnCK0 bits in the TM
control registers. The clock source can be a ratio of either the system clock f
clock f , the f clock source or the external TCKn pin. Note that setting these bits to the value 101
H TBC
will select a reserved clock input, in effect disconnecting the TM clock source. The TCKn pin clock
source is used to allow an external signal to drive the TM as an external clock source or for event
counting.
TM Interrupts
The Compact and Standard type TMs each have two internal interrupts, one for each of the internal
comparator A or comparator P, which generate a TM interrupt when a compare match condition
occurs. As the Enhanced type TM has three internal comparators and comparator A or comparator
B or comparator P compare match functions, it consequently has three internal interrupts. When a
TM interrupt is generated it can be used to clear the counter and also to change the state of the TM
output pin.
TM External Pins
Each of the TMs, irrespective of what type, has one TM input pin, with the label TCKn. The TM
input pin, is essentially a clock source for the TM and is selected using the TnCK2~TnCK0 bits in
the TMnC0 register. This external TM input pin allows an external clock source to drive the internal
TM. This external TM input pin is shared with other functions but will be connected to the internal
TM if selected using the TnCK2~TnCK0 bits. The TM input pin can be chosen to have either a
rising or falling active edge. The TMs each have one or more output pins with the label TPn. When
the TM is in the Compare Match Output Mode, these pins can be controlled by the TM to switch
to a high or low level or to toggle when a compare match situation occurs. The external TPn output
pin is also the pin where the TM generates the PWM output waveform. As the TM output pins are
pin-shared with other function, the TM output function must first be setup using registers. Asingle
bit in one of the registers determines if its associated pin is to be used as an external TM output
pin or if it is to have another function. The number of output pins for each TM type and device is
different, the details are provided in the accompanying table.
All TM output pin names have a "_n" suffix. Pin names that include a "_1" or "_2" suffix indicate
that they are from a TM with multiple output pins. This allows the TM to generate a complimentary
output pair, selected using the I/O register data bits.
Rev. 2.10
HT68F20/HT68F30/HT68F40/HT68F50/HT68F60
HT68FU30/HT68FU40/HT68FU50/HT68FU60
Enhanced I/O Flash Type 8-Bit MCU with EEPROM
98
or the internal high
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