MC68HC05BD3 Datasheet, PDF (41/112 Pages) Motorola, Inc – HCMOS microcontroller

5
MULTI-FUNCTION TIMER
The MFT provides miscellaneous functions to the MC68HC05BD3 MCU. It includes a timer
overflow function, real-time interrupt, and COP watchdog. The external interrupt (IRQ) triggering
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option is also set by this module’s MFT Control and Status Register.
The clock base for this module is derived from the bus clock divided by four. For a 2MHz E (CPU)
clock, the clock base is 0.5MHz. This clock base is then divided by an 8-stage ripple counter to
generate the timer overflow. Timer overflow rate is thus E/1024. The output of this 8-stage ripple
counter then drives a 4-stage divider to generate real time interrupt. Hence, the clock base for real
time interrupt is E/16384. Real time interrupt rate is selected by RT0 and RT1 bits of MFT Control
and Status register. The interrupt rates are E/16384, (E/16384)/2, (E/16384)/4, and (E/16384)/8.
The selected real time interrupt rate is then divided by 8 to generate COP reset.
5.1
MFT Counter Register
The MFT counter register (MFTCR) can be read at location $0009. It is cleared by reset.
5.2
MFT Control and Status Register
Address bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
State
on reset
MFT Control and Status Register $1C TOF RTIF TOFIE RTIE IRQN
RT1 RT0 0000 0011
Register bit definitions:
TOF - Timer Overflow
1 (set) – 8-bit ripple timer overflow has occurred.
0 (clear) – No 8-bit ripple timer overflow has occurred.
MC68HC05BD3
MULTI-FUNCTION TIMER
TPG
MOTOROLA
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