HC705RC17GRSSLASHD datasheet(63/126 Pages) NXP

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Core Timer

Core Timer Counter Register

MC68HC705RC17 — Rev. 2.0

General Release Specification

Core Timer

8.4 Core Timer Counter Register

The timer counter register is a read-only register that contains the

current value of the 8-bit ripple counter at the beginning of the timer

chain. This counter is clocked by the CPU clock (E/4) and can be used

for various functions, including a software input capture. Extended time

periods can be attained using the TOF function to increment a temporary

RAM storage location, thereby simulating a 16-bit (or more) counter.

The power-on cycle clears the entire counter chain and begins clocking

the counter. After 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 starts counting

up from zero and normal device operation begins. When RESET is

asserted any time during operation (other than POR and low-power

reset), the counter chain is cleared.

8.5 Computer Operating Properly (COP) Reset

The COP watchdog timer function is implemented on this device 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 normal reset vector is fetched.

Preventing a COP time out or clearing the COP is accomplished by

writing a 0 to bit 0 of address $3FF0. When the COP is cleared, only the

final divide-by-eight stage (output of the RTI) is cleared.

Address:

$0009

Bit 7

654321

Bit 0

Read:

Write:

Reset:

00000000

= Unimplemented

Figure 8-3. Core Timer Counter Register (CTCR)

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

HC705RC17GRS/D Datasheet(PDF) 63 Page - NXP Semiconductors