Semiconductor integrated circuit and communication control apparatus
First Claim
1. A semiconductor integrated circuit comprising:
- a CPU having a control program which causes said CPU to;
process data using reference clock pulses from an externally connected oscillator,automatically cut off said reference clock pulses to said CPU when a specified condition is satisfied during the performance of said processing so that said CPU enters a sleep state, andresume said process by applying said reference clock pulses to said CPU upon receiving a start signal so that said CPU exits said sleep state; and
a timer circuit, coupled to said CPU comprising;
an oscillation circuit composed of at least a capacity element, a resistance element and a semiconductor element, said oscillation circuit generating second clock pulses without using an externally connected oscillator; and
sleep time determining means for counting said second clock pulses from a start count value, and generating said start signal when a count value reaches a specified value;
wherein said CPU includes sleep time calibrating means for correcting said start count value before said CPU enters said sleep state based on a time error contained in said second clock pulses with respect to said reference clock pulses or reference signals externally inputted at a specified time interval.
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Accused Products
Abstract
A semiconductor integrated circuit, which can precisely measure the sleep time of a CPU by using a built-in oscillation circuit which does not utilize an oscillator to automatically activate the CPU, is disclosed. A communication control part of a responder mounted on a vehicle, which composes a toll road charging system, is composed of an LSI having a built-in CPU with a sleep function for automatically stopping operation clocks. The CPU is held in the sleep state for a certain time period from the time when the responder completes data communications with a ground station until the time when the responder exits the communication area of the ground station. The sleep time is measured by having a dividing counter downcount oscillation signals from a CR oscillation circuit built in the LSI. However, as the oscillation frequency of the CR oscillation circuit varies according to the operational environment, such as temperature, the CPU obtains the frequency error of the second clock pulses and correct the count value for sleep time measurement based on the reference clock pulses from a quartz oscillator, which becomes the operation clocks of its own, immediately before entering the sleep state.
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Citations
18 Claims
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1. A semiconductor integrated circuit comprising:
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a CPU having a control program which causes said CPU to; process data using reference clock pulses from an externally connected oscillator, automatically cut off said reference clock pulses to said CPU when a specified condition is satisfied during the performance of said processing so that said CPU enters a sleep state, and resume said process by applying said reference clock pulses to said CPU upon receiving a start signal so that said CPU exits said sleep state; and a timer circuit, coupled to said CPU comprising; an oscillation circuit composed of at least a capacity element, a resistance element and a semiconductor element, said oscillation circuit generating second clock pulses without using an externally connected oscillator; and sleep time determining means for counting said second clock pulses from a start count value, and generating said start signal when a count value reaches a specified value; wherein said CPU includes sleep time calibrating means for correcting said start count value before said CPU enters said sleep state based on a time error contained in said second clock pulses with respect to said reference clock pulses or reference signals externally inputted at a specified time interval. - View Dependent Claims (2, 3, 4, 5, 13, 14, 15, 16, 17, 18)
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6. A communication control apparatus comprising:
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a communication circuit for receiving communication signals through an antenna; a CPU, coupled to the communication circuit, for performing processing when the communication signals are received from the communication circuit and for entering a sleep state when a condition has been satisfied upon the completion of the processing; and timer means, coupled to the CPU, including a self oscillator comprising a semiconductor element for generating clock pulses without using a crystal oscillator, and measuring a sleep time of the CPU by counting the clock pulses; the CPU including sleep time calibrating means for correcting a clock count value of the timer means only once by obtaining an error contained in the clock pulses based on reference signals externally inputted at a specified time interval upon the determination that the condition for the CPU for entering the sleep state has been satisfied. - View Dependent Claims (7, 8, 9, 10, 11, 12)
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Specification