MC68HC705BD3 FREESCALE [Freescale Semiconductor, Inc], MC68HC705BD3 Datasheet - Page 41

• Manufacturer Part Number: MC68HC705BD3
• Description: High-density complementary metal oxide semiconductor (HCMOS) microcontroller unit
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

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
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
The MFT counter register (MFTCR) can be read at location $0009. It is cleared by reset.
5.2
Register bit definitions:
TOF - Timer Overflow
MC68HC05BD3
MFT Control and Status Register
1 (set)
0 (clear) –
MFT Counter Register
MFT Control and Status Register
–
MULTI-FUNCTION TIMER
8-bit ripple timer overflow has occurred.
No 8-bit ripple timer overflow has occurred.
Address bit 7
$1C
MULTI-FUNCTION TIMER
TOF
RTIF
bit 6
5
TOFIE
bit 5
RTIE
bit 4
IRQN
bit 3
bit 2
bit 1
RT1
bit 0
RT0
0000 0011
on reset
State
TPG
5-1
5