Holtek BS83B24C Manual page 145

BS83B24C/BS83C40C
Touch Flash MCU
During this reference clock fixed interval, the number of clock cycles generated by the sense
oscillator is measured, and it is this value that is used to determine if a touch action has been made
or not. At the end of the fixed reference clock time interval a Touch Key interrupt signal will be
generated.
Using the TSCS bit in the TKC1 register can select the module 0 time slot counter as the time slot
counter for all modules. All modules use the same started signal, TKST, in the TKC0 register. The
touch key module 16-bit C/F counter, touch key function 16-bit counter, 5-bit time slot unit period
counter in all modules will be automatically cleared when the TKST bit is cleared to zero, but the 8-bit
programmable time slot counter will not be cleared. The overflow time is setup by user. When the
TKST bit changes from low to high, the 16-bit C/F counter, touch key function 16-bit counter, 5-bit
time slot unit period counter and 8-bit time slot timer counter will be automatically switched on.
The key oscillator and reference oscillator in all modules will be automatically stopped and the
16-bit C/F counter, touch key function 16-bit counter, 5-bit time slot unit period counter and 8-bit
time slot timer counter will be automatically switched off when the time slot counter overflows.
The clock source for the time slot counter is sourced from the reference oscillator or f
selected using the MnTSS bit in the TKMnC1 register. The reference oscillator and key oscillator
will be enabled by setting the MnROEN bit and MnKOEN bits in the TKMnC1 register.
When the time slot counter in all the touch key modules or in the touch key module 0 overflows,
an actual touch key interrupt will take place. The touch keys mentioned here are the keys which are
enabled.
Each touch key module consists of four touch keys, KEY1~KEY4 are contained in module 0,
KEY5~KEY8 are contained in module 1, KEY9~KEY12 are contained in module 2, etc. Each touch
key module has an identical structure.
Auto Scan Mode
There are two scan modes contained for the touch key function, the auto scan mode and the manual
scan mode which are selected using the TKMOD bit in the TKC0 register. The auto scan mode can
minisize the load of the application program and improve the touch key scan operation performance.
When the TKMOD bit is cleared to 0, the auto scan mode is selected to scan the module keys in a
specific sequence determined by the MnSK3[1:0]~MnSK0[1:0] bits in the TKMnC2 register.
In the auto scan mode the key oscillator and reference oscillator will automatically be enabled when
the TKST bit is set from low to high and disabled automatically when the TKBUSY bit changes
from high to low. When the TKST bit is set from low to high in the auto scan mode, the internal
capacitor value of the reference oscillator for the selected key to be scanned in the time slot 0 will
first be read from a specific location of the dedicated touch key data memory and loaded into the
corresponding TKMnROH/TKMnROL registers. Then the 16-bit C/F counter value will be written
into the corresponding location of the time slot 3 scanned key in the touch key data memory. After
this, the selected key will start to be scanned in time slot 0. At the end of the time slot 0 key scan
operation, the reference oscillator internal capacitor value for the next selected key will be read from
the touch key data memory and loaded into the next TKMnROH/TKMnROL registers. Then the
16-bit C/F counter value of the current scanned key will be written into the corresponding touch key
data memory. The whole auto scan operation will sequentially be carried out in the above specific
way from time slot 0 to time slot 3. At the end of the time slot 3 key scan operation, the reference
oscillator internal capacitor value for the time slot 0 selected key will again be read from the touch
key data memory and loaded into the corresponding TKMnROH/TKMnROL registers. Then the
16-bit C/F counter value will be written into the relevant location of the time slot 3 scanned key in
the touch key data memory. After four selected keys are scanned, the TKRCOV bit will be set high
and the TKBUSY bit will be set low as well as an auto scan mode operation is completed.
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