參數(shù)資料
型號: MC68HC05F4FB
廠商: MOTOROLA INC
元件分類: 微控制器/微處理器
英文描述: 8-BIT, MROM, 1.789 MHz, MICROCONTROLLER, PQFP44
封裝: QFP-44
文件頁數(shù): 78/130頁
文件大?。?/td> 2089K
代理商: MC68HC05F4FB
MC68HC05F4
MOTOROLA
6-1
16-BIT PROGRAMMABLE TIMER
6
16-BIT PROGRAMMABLE TIMER
The timer consists of a 16-bit read-only free-running counter, with a xed divide-by-four prescaler,
plus the input capture/output compare circuitry. The timer can be used for many purposes
including measuring pulse length of two input signals and generating two output signals. Pulse
lengths for both input and output signals can vary from several microseconds to many seconds.
The timer is also capable of generating periodic interrupts or indicating passage of an arbitrary
multiple of four CPU cycles. A block diagram is shown in Figure 6-1, and timing diagrams are
The timer has a 16-bit architecture, hence each specic functional segment is represented by two
8-bit registers. These registers contain the high and low byte of that functional segment. Accessing
the low byte of a specic timer function allows full control of that function; however, an access of
the high byte inhibits that specic timer function until the low byte is also accessed.
The 16-bit programmable timer is monitored and controlled by a group of fteen registers, full
details of which are contained in this section.
Note:
A problem may arise if an interrupt occurs in the time between the high and low bytes
being accessed. To prevent this, the I-bit in the condition code register (CCR) should be
set while manipulating both the high and low byte register of a specic timer function,
ensuring that an interrupt does not occur.
6.1
Counter
The key element in the programmable timer is a 16-bit, free-running counter or counter register,
preceded by a prescaler that divides the internal processor clock by four. The prescaler gives the
timer a resolution of 2
s if the internal bus clock is 2 MHz. The counter is incremented during the
low portion of the internal bus clock. Software can read the counter at any time without affecting
its value.
TPG
47
05F4Book Page 1 Tuesday, August 5, 1997 1:10 pm
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PDF描述
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