XC68HC705JB3 Motorola, XC68HC705JB3 Datasheet - Page 54

• Manufacturer Part Number: XC68HC705JB3
• Description: MICROCONTROLLER
• Manufacturer: Motorola

GENERAL RELEASE SPECIFICATION
8.1
8.2
8.3
8.3.1 Timer Counter Register (TCNT) $09
MOTOROLA
8-2
OVERVIEW
As shown in Figure 8-1, the Timer is driven by the timer clock, NTF1, divided by
four. NTF1 has the same phase and frequency as the processor bus clock, PH2,
but continues to run in WAIT mode. The NTF1 drives an 8-bit ripple counter. The
value of this 8-bit ripple counter can be read by the CPU at any time by accessing
the Timer Counter Register (TCNT) at address $09. A timer overflow function is
implemented on the last stage of this 8-bit counter, giving a possible interrupt rate
of f
The last stage of the 8-bit counter also drives a further 7-bit counter. The final four
stages is used by the RTI circuit, giving possible RTI rates of f
2
RTI and CTOF enable bits and flags are located in the Timer Control and Status
Register at location $08.
The power-on cycle clears the entire counter chain and begins clocking the
counter. After 224 or 4064 cycles, the power-on reset circuit is released which
again clears the counter chain and allows the device to come out of reset. At this
point, if RESET is not asserted, the timer will start counting up from zero and nor-
mal device operation will begin. If RESET is asserted at any time during operation
the counter chain will be cleared.
COMPUTER OPERATING PROPERLY (COP) WATCHDOG
The COP Watchdog is enabled by a mask option.
The COP Watchdog Timer function is implemented by using the output of the RTI
circuit and further dividing it by eight. The minimum COP reset rates are listed in
Table 8-1. If the COP circuit times out, an internal reset is generated and the nor-
mal reset vector is fetched.
Preventing a COP time-out is done by writing a “0” to bit-0 of address $1FF0.
When the COP is cleared, only the final divide by eight stage (output of the RTI) is
cleared.
MFT REGISTERS
The Timer Counter Register is a read-only register which contains the current
value of the 8-bit ripple counter at the beginning of the timer chain. This counter is
clocked at f
capture. Extended time periods can be attained using the CTOF function to incre-
ment a temporary RAM storage location thereby simulating a 16-bit (or more)
counter. The value of each bit of the TCNT is shown in Figure 8-2. This register is
cleared by reset.
17
OP
, selected by RT1 and RT0 (see Table 8-1). The RTI rate selector bits, and the
÷1024.
OP
÷4 and can be used for various functions including a software input
MULTI-FUNCTION TIMER
November 5, 1998
OP
÷2
14
MC68HC05JB3
, 2
15
, 2
REV 1
16
or