MC68HC05T16 Datasheet, PDF (52/128 Pages) Motorola, Inc – High-density complementary metal oxide semiconductor (HCMOS) microcontroller unit

5.2
MULTI-FUNCTION TIMER
Multi-Function Timer Register
Address bit 7
$1C TOF
bit 6 bit 5 bit 4 bit 3 bit 2 bit 1
RTIF TOFIE RTIE IRQN WDOG RT1
bit 0
State
on reset
RT0 0000 0011
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 4.2 MHz E (CPU)
clock, the clock base is 1.05 MHz. This clock base is then divided by an 8-stage ripple counter to
5
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
1 (set) – 8-bit ripple timer overflow has occurred.
0 (clear) – No 8-bit ripple timer overflow has occurred.
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
1 (set) – A real time interrupt has occurred.
0 (clear) – A real time interrupt has not occurred.
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
1 (set) – TOF interrupt is enabled.
0 (clear) – TOF interrupt is disabled.
RTIE - Real Time Interrupt Enable
1 (set) – Real time interrupt is enabled.
0 (clear) – Real time interrupt is disabled.
MOTOROLA
5-10
TIMERS
TPG
MC68HC05T16