参数资料
型号: MC68HC705V8B
厂商: FREESCALE SEMICONDUCTOR INC
元件分类: 微控制器/微处理器
英文描述: 8-BIT, OTPROM, 2.1 MHz, MICROCONTROLLER, PDIP56
封装: SDIP-56
文件页数: 166/172页
文件大小: 890K
代理商: MC68HC705V8B
MOTOROLA
SECTION 12: CORE TIMER
Page 82
MC68HC705V8 Specification Rev. 2.1
As seen in Figure 6-1, the internal peripheral clock is divided by four then 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 Core Timer Counter Register (CTCR) at address $09. A timer overflow
function is implemented on the last stage of this counter, giving a possible interrupt rate of
the Internal Peripheral clock(E)/1024. This point is then followed by two more stages, with
the resulting clock (E/2048) driving the Real Time Interrupt circuit (RTI). The RTI circuit
consists of three divider stages with a 1 of 4 selector. The output of the RTI circuit is further
divided by eight to drive the mask optional COP Watchdog Timer circuit. The RTI rate
selector bits, and the RTI and CTOF enable bits and flags are located in the Timer Control
and Status Register at location $08.
12.1
CORE TIMER CTRL & STATUS REGISTER (CTCSR) $08
The CTCSR contains the timer interrupt flag, the timer interrupt enable bits, and the real
time interrupt rate select bits. Figure 12-2 shows the value of each bit in the CTCSR when
coming out of reset.
Figure 12-2:
Core Timer Control and Status Register
12.1.1
CTOF - Core Timer Over Flow
CTOF is a read-only status bit set when the 8-bit ripple counter rolls over from $FF to $00.
Clearing the CTOF is done by writing a ‘1’ to TOFC. Writing to this bit has no effect. Reset
clears CTOF.
12.1.2
RTIF - Real Time Interrupt Flag
The Real Time Interrupt circuit consists of a three stage divider and a 1 of 4 selector. The
clock frequency that drives the RTI circuit is E/2**11 (or E/2048) with three additional
divider stages giving a maximum interrupt period of 7.8 milliseconds at a bus rate of 2.1
MHz. RTIF is a clearable, read-only status bit and is set when the output of the chosen (1
of 4 selection) stage goes active. Clearing the RTIF is done by writing a “1” to RTFC.
Writing has no effect on this bit. Reset clears RTIF.
12.1.3
TOFE - Timer Over Flow Enable
When this bit is set, a CPU interrupt request is generated when the CTOF bit is set. Reset
clears this bit.
12.1.4
RTIE - Real Time Interrupt Enable
When this bit is set, a CPU interrupt request is generated when the RTIF bit is set. Reset
clears this bit.
12.1.5
TOFC - Timer Over Flow Flag Clear
When a “1” is written to this bit, CTOF is cleared. Writing a “0” has no effect on the CTOF
bit. This bit always reads as zero.
CTOF
TOFE
RTIE
TOFC
RTFC
RT1
RT0
RTIF
$08
0
000011
0
RESET:
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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