MICROCOMPUTER PROVIDED WITH BUILT-IN CONVERTER

Abstract: A microcomputer provided with a built-in converter, provided with a CPU (10) which processes digital signals according to program instructions and a converter (30) (an AD or a DA converter) which, for the input or output of the CPU (10), converts an analog signal to a digital signal, or vice versa, has a conversion controlling circuit (40) which controls the operation of the converter (30) according to the controlling output of the CPU (10) and outputs an operation stopping signal to the CPU (10) in a specified period of the operation of the converter (30) (e.g., a period affecting the conversion accuracy of the converter during the converting operation thereof).

Description: Industrial Field The present invention relates to a microcomputer with built-in converters, and more particularly relates to a microcomputer which prevents degradation of conversion accuracy due to noises which is provided with built-in type analog to digital converters (hereinafter referred to as "AD converters"), digital to analog converters (hereinafter referred to as "DA converters"), or a combination of these converters. Background of the Invention One typical example of such a conventional microcomputer is disclosed in Japanese Laid Open Publication No. 64-58043. Its configuration will be explained hereinafter referring to drawings. Fig. 2 is a block diagram of one example of the conventional microcomputer with built-in converters. This microcomputer incorporates a central processing unit (hereinafter referred to as "CPU") 1 which is adapted for processing digital signals in response to instructions provided by a given programme. An AD converter 2 is connected to this CPU 1 via a data bus DB and an address bus AB. The AD converter 2 converts each analog signal received at an analog input terminal 3 to a corresponding digital signal in accordance with a conversion initiation signal ST from the CPU 1. After the conversion, the AD converter 2, on one hand, passes the digital signal to the CPU 1 via the data bus DB and, on the other hand, generates an AD selection signal S2. An edge detection circuit 4 is connected to the CPU 1 as well as to the AD converter 2. The edge detection circuit 4 detects state of conversion of the AD converter 2 in response to the AD selection signal S2 and has a function to pass a CPU stop signal SP or stop clear signal CLR to the CPU 1. In the case of a microcomputer of this type, the CPU 1 passes, via the address bus AB, to the AD converter 2 each address which was advancedly allotted to the AD converter 2 by the given programme. Thereupon, selection is carried out regarding the AD converter 2 and an AD selection signal S2 generated by the selected AD converter 2 becomes active, i.e. shifts from an "L" level to a "H" level. The edge detection circuit 4 detects a rise of the AD selection signal S2, i.e. from the "L" level to the "H" level and passes the CPU stop signal SP to the CPU 1 to require halt of CPU operation. On receipt of the CPU stop signal SP, the CPU 1 is put in a stop mode and concurrently passes the AD conversion initiation signal ST to the AD converter 2 to initiate its operation. As a result, the AD converter 2 converts an analog signal received at the analog input terminal 3 to a corresponding digital signal. After passage of a prescribed period, the AD selection signal S2 outputted from the AD converter 2 shifts from the "H" level to the "L" level. This shift in level is detected by the edge detection circuit 4 which in turn passes the stop clear CLR to the CPU 1 so that the CPU 1 restarts its operation. As stated above, the conventional microcomputer is associated with the edge detection circuit 4 which detects the conversion carried out by the AD converter 2 so that, when the AD converter 2 is in operation, the edge detection circuit 4 outputs a CPU stop signal SP to halt major operations of the CPU 1. Consequently, generation of noises by the CPU 1 during the AD conversion is reduced to raise the operation accuracy of the AD converter 2. In the case of the microcomputer of the above-described construction, however, the CPU 1 is put in a halt mode during operation by the AD converter 2 (or alternatively a DA converter) and, as a result, the CPU 1 cannot perform any operations other than the AD conversion (or alternatively DA conversion), thereby causing a serious problem of low operation efficience of the CPU 1. When a microcomputer is provided with a halt mode for halting run of the CPU itself, a similar operation can be carried out by an appropriate programme without use of the edge detection circuit 4. It is the basic object of the present invention to provide a microcomputer with built-in converters which assures high accuracy in AD or DA conversion without increase of circuit size and any significant degradation in CPU operation efficiency. JP-A-64-58044 discloses a device where a control circuit recognizes the presence of a high-accuracy conversion instruction and hence determines a stop period for the CPU. Disclosure of the Invention The present invention is defined in independent claims 1 and 3. The dependent claims define particular embodiments thereof. A conversion control circuit is incorporated in a microcomputer which is provided with a CPU adapted for processing digital signal under control by programme instructions and AD or DA converters adapted for conversion between analog and digital signals. The conversion control circuit controls operation of the converters in response to a control output from the CPU and passes an operation halt signal to the CPU during a specified period related to the converters, e.g. a period in which an influence appears on conversion accuracy during operation of the converters. With this construction, the conversion control circuit controls operation of the converters on receipt of a conversion initiation instruction which is generated by the CPU following the programme instructions. Each converter passes a digital signal to the CPU after conversion from a corresponding input analog signal or, alternatively, generates an analog signal after conversion from a corresponding digital signal received from the CPU. During this conversion, the conversion control circuit passes the operation halt signal to the CPU only over the specified period in which conversion is most influenced by noises. Thereupon, the CPU halts its operation only during the specified period. Thanks to this halt of CPU operation, malign influence of the noises on the converter is mitigated and the conversion accuracy of the converter is much improved. In addition, the CPU operation can be performed even during the conversion so as to improve the operation efficiency of the CPU, thereby solving the aforementioned problems. Brief Description of the Drawings Fig. 1 is a circuit diagram of the main part of an AD converter utilized in the microcomputer in accordance with the present invention, Fig. 2 is a block diagram of one example of the conventional microcomputer with built-in converters, Fig. 3 is a block diagram of the main part of one embodiment of the microcomputer in accordance with the present invention, and Fig. 4 is a timing diagram of various signals processed in the microcomputer shown in Figs. 1 and 3. Description of the Preferred Embodiments One embodiment of the microcomputer in accordance with the present invention is shown in Fig. 3 in which the microcomputer is provided with a CPU 10 adapted for running programmes stored in its memories (not shown). The CPU 10 includes an operator section for performing arithmetic and logic operations, a controller section for controlling all operations of the CPU and a register section functioning as an internal memory. The CPU 10 passes AD initiation data to an AD converter section 20 via a data bus DBn. The CPU 10 further passes writing signals W, reading signals R and clock pulses CLK to the AD converter section 20. On receipt of the operation stop signal SP, the CPU 10 halts all of its main operations except for output of the clock pulses. On receipt of the AD conversion initiation data and the writing signal W from the CPU 10 via the data bus DBn, the AD converter section 20 operates to convert an analog signal Ain received at an analog input terminal 21 to a corresponding digital signal. During conversion, the AD converter section 20 generates an operation halt signal ADHLT over a specified period in which influence appears on its conversion accuracy. The output terminal for this operation halt signal ADHLT is connected to an input terminal D of a delay-type flip-flop (hereinafter referred to as "D-FF") 50. The clock pulses CLK from the CPU 10 is inputted to a clock pulse input terminal of D-FF 50 and the operation stop signal SP appearing at its output terminal Q is supplied to the CPU 10. The D-FF 50 initiates its operation at every falling of the clock pulses to generate the operation stop signal SP. As shown in Fig. 1, the AD converter section 20 includes, for example, a chopper-type AD converter 30 and a conversion control circuit 40 for controlling operation of the AD converter 30. The AD converter 30 includes an inverter 31 adapted for inversion of a control signal EA used for control of analog input signals, an inverter 32 adapted for inversion of a control signal ER used for input control of a reference voltage V, an analog switch 33 adapted for input control of the analog signal Ain in accordance with the control signal EA and an output signal from the inverter 31, and an analog switch 34 adapted for input control of the reference voltage VR in accordance with the control signal ER and an output signal from the inverter 32. The analog switches 33 and 34 are connected to a comparator 36 through a capacitor 35 in common. An output terminal of the comparator 36 is connected to an input terminal D of a latch circuit 37. The latch circuit 37 latches an output signal from the comparator 36 in response to a latch signal Wout received at its latch input terminal L. After the latching, digital signals Dout, which corresponds to latched data, appears at an output terminal Q. The digital signals Dout are sequentially stored at a register (not shown) over the bit number of the AD converter. Thereafter, the digital signals Dout are passed to the CPU 10 via the data bus DBn shown in Fig. 3. The conversion control circuit 40 incorporates a dual input AND-gate 41 which receives the writing signal W and clock pulses CLK from the CPU 10. The output terminal of the AND-gate 41 is connected to a clock input terminal of a D-FF 42. When the writing signal W received from the CPU 10 falls, the D-FF 42 reads information on the data bus DBn through its input terminal D and generates a conversion initiation signal S42 at its output terminal Q. The D-FF 42 is involved in control of initiation of operation of the conversion control circuit 40 as well as in initialization of the conversion control circuit 40 in response to a conversion termination signal COVEND received at its reset terminal R. The output terminal Q of the D-FF 42 is connected to respective reset terminals of a D-FF 44 and a counter 45 such as a Johnson counter through the inverter 43. The D-FF 44 is adapted for dividing each clock pulse CLK into two received at its clock input terminal to output through its output terminal Q. The outputs from the D-FF 44 is supplied as clock pulses to the counter 45. The counter 45 includes, for example, four sets of D-FFs 45a to 45d connected in series. An output terminal Q of the last stage D-FF 45d is connected to an input terminal D of the first stage D-FF 45a. A logic circuit 46 is connected to an output terminal of the counter 45. Depending on a logic value of the output signal from the counter 45, the logic circuit 46 outputs the control signals EA and ER, the latch signal Wout and the conversion halt signal ADHLT. The logic circuit 46 includes dual-input AND-gates 46a to 46e and a dual-input OR-gate 46f. Fig. 4 depicts time-functional changes of various signals processed in the circuits shown in Figs. 1 and 3. An operation of the microcomputer in accordance with the present embodiment will be explained hereinafter in reference to the above drawings. The CPU 10 issues addresses allotted to the AD converter section 20 and AD conversion data via the data bus DBn as well as the writing signal W to initiate operation of the AD converter section 20. Within the AD converter section 20 shown in Fig. 1, the D-FF 42 of the conversion control circuit 40 takes up an "H" level signal from the data bus DBn when the writing signal W from the CPU 10 falls to output the conversion initiation signal S42 of an "H" level via its output terminal Q. This conversion initiation signal S42 is inverted at the inverted 43 to make the reset terminals R of the D-FF 44 and the D-FF 45a to 45d in the counter 45 to "L" levels. Then, the D-FF 44 divides by two the clock pulse CLK from the CPU 10 to generate a divided clock pulse 1/2CLK at its output terminal Q, which is then passed to the clock input terminals of the D-FF 45a to 45d in the counter 45. On receipt of the divided clock pulse 1/2CLK, the D-FF 45a to 45b perform counting operations to output counted results via the respective output terminals Q. Logics of the counted results are discerned at the AND-gates 46a to 46e and the OR-gate 46f to generate the control signals EA and ER, the latch signal Wout and the operation halt signal ADHLT depending on the result of the logic operation. The control signal EA outputted from the AND-gate 46a assumes an "H" level when the output terminal Q of the D-FF 45a is an "H" level and the output terminal Q of the D-FF 45d is an "H" level. The control signal ER outputted from the AND-gate 46b assumes an "H" level when the output terminal Q of the D-FF 45a is an "H" level and the output terminal Q of the D-FF 45d is an "H" level. The latch signal Wout outputted from the AND-gate 46e assumes an "H" level when the output terminal Q of the D-FF 45c is an "H" level, the output terminal Q of the D-FF 45d is an "H" level and the output terminal Q of the D-FF 44 is an "H" level. The operation halt signal ADHLT outputted from the OR-gate 46f assumes an "H" level when the output terminal Q of the D-FF 45c is an "H" level and the output terminal Q of the D-FF 45d is an "H" level, or when the output terminal Q of the D-FF 45c is an "H" level and the output terminal Q of the D-FF 45d ia at "H" level, respectively. Thus, since the conversion initiation signal S42 outputted from the D-FF 42 assumes an "H" level, the control signal EA assumes the "H" with a delay of 2CLK and the analog switch 33 becomes an on state via the inverter 31 in the AD converter 30. Since the control signal ER is at an "L" level at this moment, the analog switch 34 is in an off state in the AD converter 30. When the analog switch 33 turns to an off state, the analog signal Ain received at the analog input terminal 21 is passed to the capacitor 35 via the analog switch 33 for its charge. After holding the "H" level over a period of 6CLK, the control signal EA assumes an "L" level and, as a consequence, the analog switch 33 turns to an off state. With a delay of 2CLK, the control signal ER assumes an "H" level to make the analog switch 34 on state. Then a reference voltage VR, which is generated by a certain analog circuit (not shown) in the conversion control circuit 40, is applied to the capacitor 35 via the analog switch 34. Comparison is performed between the analog signal Ain charged in the capacitor 35 and the reference voltage VR by the comparator 36 which in turn passes a result of comparison to the input terminal D of the latch circuit 37. Latching by the latch circuit 37 is carried out in response to a latch signal Wout of and "H" level with a delay of 6CLK after the control signal ER has assumed the "H" level. After holding the "H" level for a period of 6CLK, the control signal ER shift to an "L" level and, after passage of a period of 2CLK, the control signal EA assumes an "H" level. The AD converter 30 repeats the above-described operation to the maximum bit number of its resolving power and, thereafter terminates AD conversion. When the AD converter 30 has, for example a resolving power of maximum 10 bits, a period of 16CLK is necessary for AD conversion of 1 bit as shown in Fig. 4 and, as a result, the AD converter 30 terminates its operation after a total period of 160CLK. As the operation is terminated, the conversion termination signal COVEND is generated by an appropriate circuit (not shown) contained in the conversion control circuit 40, which resets the D-FF 42. The conversion initiation signal S42 is inverted at the inverter 43 to assume an "H" level, which resets the D-FF 44 and 45a to 45d. Thus, each output terminal Q assumes an "L" level whereas each inverted output terminals Q assumes an "H" level. As a result, the conversion control circuit 40 is initialized to terminate the AD conversion. The digital signals Dout from the output terminal Q of the latch circuit 37 are sequentially stored in a register (not shown) for the bit number of the AD converter and, on receipt of a reading signal from the CPU 10, passed the CPU 10 via the data bus DBn. When the CPU 10 continues its operation during operation of the AD converter 30, generation of noises from the CPU 10 tends to degrade AD conversion accuracy. In order to evade the inconvenience, it can be considered to interrupt the operation of the CPU10 during the AD conversion. Such interruption, however, lowers operation efficiency of the CPU 10. Here, it should be appreciated that the period of accuracy degradation by noise generation is limited in the time span of the AD conversion by the AD converter 30. When noises are generated just before termination of analog input charge to the capacitor 35 shown in Fig. 1, no charge can be carried out at a normal voltage level. Further, when noises are generated just before termination of comparison between the analog input charged at the capacitor 35 and the reference voltage, i.e. just before latching of the result of the comparison by the latch circuit 37, no comparison can be carried out at a normal voltage level. In contrast to this, generation of noises at rising of the control signal EA in Fig. 4 and the early half of the signal period has no substantial influence on conversion accuracy as long as there is no substantial noise generation during the later half of the signal period. In accordance with the present invention, the conversion halt signal ADHLT outputted from the OR-gate 46f in Fig. 1 is forced to assume an "H" level during operation of the AD converter 30, in particular during the above-described limited period of significant noise influence. This "H" level conversion signal ADHLT is then passed to the input terminal D of the D-FF 50 in Fig. 3. Then, the D-FF 50 takes in the conversion halt signal ADHLT at rising of each clock pulse CLK from the CPU 10 to shift the CPU stop signal SP, which is passed to the CPU 10 via its output terminal Q, to an "H" level. On receipt of this stop signal SP, the CPU 10 ceases all of its operations except for generation of the clock pulses CLK. As stated above, major operations of the CPU 10 are interrupted by the CPU stop signal SP only during the limited period of significant noise influence during conversion by the AD converter 30. This specified interruption in CPU operation reliably prevent degradation in conversion accuracy which would be otherwise caused during AD conversion. In addition, thanks to a relatively small length of the interruption, the CPU 10 is allowed to be involved in operations other than the AD conversion. As a consequence, AD conversion can be carried out at high degree of accuracy without causing no substantial lowering in operation efficiency of the CPU 10. The present invention is not limited to be applied to the embodiments illustrated in the drawings. Some other variations are as follows; (a) The AD converter 30 shown in Fig. 1 may be given in the form of a serial comparison type AD converter. The conversion control circuit 40 can also be more or less varied by us of other types of flip-flop and/or gate circuits. (b) The D-FF 50 in Fig. 3 may be incorporated in the AD converter section 20 or in the CPU 10. (c) The AD converter section 20 is connected to the CPU 10 in the case of the foregoing embodiments. Alternatively, one of DA converters may be additionally connected to the CPU 10. As an alternative for the AD converter section 20, a DA converter section may be connected to the CPU 10. Applicability for the Industry In accordance with the present invention, major operations of a CPU is interrupted by a CPU stop signal only during a limited period of significant noise influence. As a consequence, degradation in conversion accuracy by CPU noises is reliably prevented. Since the length of interruption is quite limited, CPU is able to carry out other operations in addition to the conversion. High level of conversion accuracy is assured with no substantial loss in operation efficiency.

Claims: A microcomputer having a central processing unit (10) to process digital signals under control of program instructions and an analog to digital (A/D) converter (20) to perform conversion between analog and digital signals, comprising: a first node (21) to receive analog signals; a second node to receive a reference voltage (VR); a counter (45) responsive to a clock signal to define a first period and a second period after said first period; a first switch (33) to apply said analog signals received at said first node to said A/D converter during said first period; a second switch (34) to apply said reference voltage received at said second node to said A/D converter during said second period; and a halting circuit (40), said halting circuit being adapted to interrupt operation of said central processing unit during a third period, the third period including the final part of said first period and being shorter than said first period, said halting circuit further interrupting the operation of said central processing unit during a fourth period, the fourth period including the final part of said second period and being shorter than said second period. A microcomputer according to claim 1, wherein said third and fourth periods endure for limited times beyond the end of said first and second periods, respectively. A method of processing digital signals in a central processing unit (10) of a microcomputer under control of program instructions, said microcomputer having an analog to digital (A/D) converter (20) to perform conversion between analog and digital signals, comprising the steps of: receiving analog signals by a first node (21); receiving a reference voltage (VR) by a second node; defining a first period and a second period after said first period by means of a counter (54) responsive to a clock signal; applying to the A/D converter by means of a first switch (33) said analog signals during a first period and by means of a second switch (34) said reference voltage (VR) during a second period after said first period; halting the operation of said central processing unit (10) during a third period, the third period including a final part of said first period and being shorter than said first period, and further interrupting the operation of said central processing unit (10) during a fourth period, the fourth period including the final part of said second period and being shorter than said second period. A method according to claim 3, wherein said third and fourth periods endure for limited times beyond the end of said first and second periods, respectively.

Inventors: ABE SYUNJI, KOBAYASHI JIRO, SUWABE SATORU, ABE, SYUNJI, KOBAYASHI, JIRO, SUWABE, SATORU, ABE, SYUNJI, OKI ELECTRIC INDUSTRY CO., LTD., KOBAYASHI, JIRO, OKI ELECTRIC INDUSTRY CO., LTD., SUWABE, SATORU, OKI ELECTRIC INDUSTRY CO., LTD.
Applicants: OKI ELECTRIC IND CO LTD, OKI ELECTRIC INDUSTRY COMPANY, LIMITED
Application year: 1991
Main classification: G06F15
IPC codes: G06F15, G06F3