MC68HC705T16 MOTOROLA [Motorola, Inc], MC68HC705T16 Datasheet - Page 52

• Manufacturer Part Number: MC68HC705T16
• Description: High-density complementary metal oxide semiconductor (HCMOS) microcontroller unit
• Manufacturer: MOTOROLA [Motorola, Inc]

5
5.2
The MFT provides miscellaneous function to the MC68HC05T16 MCU. It includes a timer overflow
function, real-time interrupt, and COP watchdog. The external interrupt (IRQ) triggering option is
also set by this Multi-Function Timer register.
The clock base for this module is derived from the bus clock divided by four. For a 4.2MHz E (CPU)
clock, the clock base is 1.05 MHz. 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 Multi-Function
Timer 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.
Register bit definitions:
TOF - Timer Overflow
This bit is set when the 8-bit ripple counter overflows from $FF to $00; a timer overflow interrupt
will occur, if TOFIE (bit 5) is set. TOF is cleared by writing a ‘0’ to the bit.
RTIF - Real Time Interrupt Flag
When RTIF is set, a CPU interrupt request is generated if RITE is set. The clock frequency that
drives the RTI circuit is E/16384 giving a maximum interrupt period of 3.9ms at a bus rate of
4.2MHz. RTIF is cleared by writing a “0” to the bit.
TOFIE - Timer Overflow Interrupt Enable
RTIE - Real Time Interrupt Enable
MOTOROLA
5-10
Multi-Function Timer Register
1 (set)
0 (clear) –
1 (set)
0 (clear) –
1 (set)
0 (clear) –
1 (set)
0 (clear) –
MULTI-FUNCTION TIMER
–
–
–
–
8-bit ripple timer overflow has occurred.
No 8-bit ripple timer overflow has occurred.
A real time interrupt has occurred.
A real time interrupt has not occurred.
TOF interrupt is enabled.
TOF interrupt is disabled.
Real time interrupt is enabled.
Real time interrupt is disabled.
Address bit 7
$1C
TOF
RTIF
bit 6
TIMERS
TOFIE
bit 5
RTIE
bit 4
IRQN WDOG
bit 3
bit 2
bit 1
RT1
MC68HC05T16
bit 0
RT0
0000 0011
on reset
State
TPG