参数资料
型号: MC68HC05RC18FN
厂商: FREESCALE SEMICONDUCTOR INC
元件分类: 微控制器/微处理器
英文描述: 8-BIT, MROM, 2.1 MHz, MICROCONTROLLER, PQCC44
封装: PLASTIC, LCC-44
文件页数: 93/126页
文件大小: 1180K
代理商: MC68HC05RC18FN
Core Timer
MC68HC05RC18 Rev. 2.1
General Release Specification
Freescale Semiconductor
Core Timer
67
NON-DISCLOSURE
AGREEMENT
REQUIRED
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 and the low-power reset both serve to clear the
entire counter chain and begin clocking the counter. After 4064 cycles,
the power-on/low-power 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 a reset other than POR and low-
power reset is asserted any time during operation, the counter chain is
cleared but the 4064-cycle stabilization period is not invoked.
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 Figure 8-1. If the COP circuit
times out, an internal reset is generated and the normal reset vector is
fetched. Preventing a COP timeout, or clearing the COP is accomplished
by writing a zero 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:
D7
D6
D5
D4
D3
D2
D1
D0
Write:
Reset:
00000000
= Unimplemented
Figure 8-3. Timer Counter Register (CTCR)
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