JPH077422A - A-D conversion method - Google Patents

Abstract

(57) [Abstract] [Purpose] The present invention is equipped with an A / D converter to perform control.
Regarding the A / D conversion method in the chip microcomputer, even if the A-D conversion accuracy is required because the operation voltage of the one-chip microcomputer provided with the A-D conversion unit that can operate at a certain range of voltage is low, the high accuracy A The purpose is to be able to obtain a -D conversion value and not to waste power. [Structure] A dedicated A / D conversion circuit for performing highly accurate A / D conversion from an internal A / D conversion unit is provided outside the one-chip microcomputer, and the internal A / D conversion unit is driven according to a request instruction. The request discriminating means selects whether to drive the dedicated A-D conversion circuit. When driving the internal A-D conversion unit, the external dedicated A-D conversion circuit is stopped, when driving the external dedicated A-D conversion circuit, the internal A-D conversion unit is stopped,
When an external dedicated A-D conversion circuit is driven, an A-D converted value reading instruction is generated to read the A-D converted value.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an A-D conversion system using a one-chip microcomputer having an A-D conversion function, and more particularly, it has an A-D conversion function internally and externally and has a wide operating voltage range. The present invention relates to an AD conversion method capable of improving the accuracy of D conversion. A one-chip microcomputer used at a high operating voltage has a high accuracy of AD conversion value, but on the contrary, a one-chip microcomputer used at a low operating voltage is at A
-D conversion accuracy deteriorates. Therefore, when a one-chip microcomputer having an A-D conversion function is used in various devices, it is required to improve the A-D conversion accuracy and save power even if the operating voltage is low.

2. Description of the Related Art FIG. 8 is a block diagram of a conventional AD converter. To explain the operation, a channel selection instruction and data for controlling the start and end of the AD conversion operation are input to the AD conversion register 81 via the bus 80. The data of the channel selection instruction is given to the channel selector 82 A
Eight A input analog signals to be converted
Select one of D ports # 1 to # 8. The analog signal of the selected A-D port is compared with the output of the resistance ladder 86 by the comparator 83 and executed by switching the A-D conversion register 85 and the resistance ladder 86 under the control of the A-D control circuit 84. The −D conversion value is set in the AD conversion register 85. As a voltage for A / D conversion of such an A / D converter, V _REF is a comparator 83.
And the A-D conversion operation corresponding to this V _REF is performed. On the other hand, a rechargeable battery (secondary battery) is installed in an electronic device such as a portable personal computer, and such a battery is charged by a DC power source generated by an AC power source (using the electronic device You can also do it while). This charging operation ends when it is detected that the battery is fully charged. Therefore, it is necessary to detect the voltage of the battery by A-D conversion during charging of the battery to control charging. FIG. 9 is a diagram showing the charging characteristics of a secondary battery (for example, a NiCd battery), where the vertical axis represents voltage (V) and the horizontal axis represents time. When charging is started, the battery voltage rises as shown in the figure. To do. As a method of detecting full charge,
As shown in the figure, there is a method of detecting full charge when the peak is passed and -ΔV is dropped. This −ΔV is a weak voltage (for example, 20 millivolts per battery cell).
FIG. 10 is a block configuration for detecting the state of charge of the battery and performing control. In the figure, 90 is a battery, 91 is an operational amplifier for performing voltage level shifting, and 92 is a one-chip microcomputer (microcomputer) including an A / D converter 93 and including a RAM, a ROM and a CPU. Figure 10
In this operation, charging is performed by applying a charging power source (not shown) to the battery 90, and the voltage of the battery 90 is input to the AD converter 93 of the one-chip microcomputer 92 that controls charging. In this case, the voltage of the battery 90 is 1
Operating voltage of the chip microcomputer 92 (2.5V to 5.5V)
Since the voltage is considerably higher, it is level-shifted by the operational amplifier 91 and supplied to the one-chip microcomputer 92.
On the other hand, as a conventional technique, an A-D converter is provided inside the LSI, and a high-precision (high-priced) A-D converter is provided outside the LSI so that the two A-D converters are always operated. , There is a method in which both of the two A-D converted values are fetched by the LSI and then one of the converted values is used by switching (Japanese Patent Laid-Open No. Hei.
196720).

As described above, the one-chip microcomputer 92 provided with the A / D converter 93 has a voltage of 2.5 V or higher.
It can operate up to 5.5V, but the voltage for AD conversion (V
_REF ) also changes with the operating voltage. For this reason, when the microcomputer has to operate at 2.5V (when the microprocessor for information processing of the electronic device is for 2.5V, etc.), the A-D conversion of the internal A-D converter is performed. The working voltage (V _REF ) is also suppressed to 2.5V. FIG. 11 is an explanatory diagram of a problem. As shown in the figure, in the case where the range of the charging voltage value of the battery is 0V to 18V, in the configuration shown in FIG. 10, the operational amplifier 91 cuts 9V or less and controls the amplification factor to control the A-D converter of the one-chip microcomputer 92. 93
Are typing in. At this time, if the operating voltage of the one-chip microcomputer 92 is high (for example, 5.5 V), the AD converter 9
3 operates at 5.5 V (V _REF is 5.5 V) and the operating voltage of the one-chip microcomputer 92 is low (for example, 2.5 V).
V), the A-D converter 93 operates at 2.5 V (V _REF is 2.5 V), so the amplification factor of the operational amplifier 91 is 0.6 (5.5 V ÷ in the former case (corresponding to 5.5 V)). 9V)
In the latter case, the conversion accuracy is 0.27 (2.5V ÷ 9V), so that the conversion accuracy is half or less when the operating voltage is low compared to when the operating voltage is high. The power supply of the 1-chip microcomputer 92 may be 5.5V in consideration of the power supply of the electronic device in which the 1-chip microcomputer is mounted, but it is also necessary to support the same configuration for 2.5V. , 2.5V
When the power supply of 1 is used, it operates based on the low precision AD conversion value. If a power supply different from the one-chip microcomputer is supplied only to the A-D conversion unit to perform highly accurate operation, the circuit becomes complicated and it cannot be used in common even when the power supply changes. Therefore, A-
When the D conversion unit uses the low A-D conversion voltage (V _REF ) to perform full charge during battery charging as shown in FIG. 10 by detecting -ΔV, the full charge can be normally detected. It may not be possible, in which case the battery may be overcharged and deteriorated. On the other hand, in the technique of the above-mentioned conventional Japanese Patent Laid-Open No. 4-196720, the internal AD conversion value and the external AD conversion value are simultaneously operated and one of them is used by switching, but both A Since the -D conversion circuit is always operating, power consumption increases, and
When a device including an LSI including a conversion unit operates on a battery, there is a problem that the operating time of the battery is shortened. The present invention is a one-chip microcomputer provided with an A-D conversion unit that can operate at a voltage in a certain range, and has a high precision A-D even when the A-D conversion voltage is low and A-D conversion accuracy is required.
It is an object of the present invention to provide an A-D conversion method that can obtain a conversion value and does not consume unnecessary power.

FIG. 1 is a block diagram showing the principle of the present invention. In FIG. 1, 1 is a processing device such as a one-chip microcomputer that operates with a constant voltage width, and 2 is an A-D conversion unit that is provided in the processing device 1 and that operates as a power supply for A-D conversion. , 3 are external dedicated A-
The D conversion circuit, 4 is a signal line provided between the processing device 1 and the dedicated A-D conversion circuit 3. Further, in the processing device 1, 10 is a request discriminating means, 11 is an AD converting section driving means, 12 is a dedicated AD converting circuit driving means, and 13 is an internal A.
The -D converted value reading means, 14 is a dedicated AD converted value reading means, and 15 is a holding means for holding the read value. According to the present invention, a dedicated A-D conversion circuit that operates with high accuracy by a high A-D conversion voltage is provided outside the processing device, and the processing device has an A-D conversion value of an analog signal provided inside thereof. A-D which is not used by controlling whether it is obtained by driving the D conversion unit or by driving an external dedicated A-D conversion circuit
The conversion mechanism stops.

In FIG. 1, the processing apparatus 1 is required to have high accuracy in AD conversion (the operating voltage of the processing apparatus is low).
A request instruction of either normal accuracy (the operating voltage of the processing device 1 is high) is sufficient. When the request determination means 10 is driven in each processing cycle of the A / D conversion in the processing device 1, the request instruction is determined and the selection operation is performed. That is, when high precision is instructed, the dedicated A-D conversion circuit drive means 12 is activated, and when normal precision (or low precision) is instructed, the A-D conversion section drive means 11 is activated.
When the dedicated A / D conversion circuit driving means 12 is activated, the dedicated A / D conversion circuit 3 is driven via the signal line 4. Dedicated A-
The D conversion circuit 3 performs an AD conversion operation on the input analog signal to generate an AD conversion value. Dedicated A-
After the D conversion circuit 3 operates, the dedicated AD conversion value reading means 14 is driven. As a result, the read instruction signal is output via the signal line 4, and when the dedicated A / D conversion circuit 3 receives this, the A / D conversion value at that time is sent to the processing device 1 via the signal line 4. This A-D converted value is the processing device 1
It is held by the holding means 15 and used for control in the processing apparatus 1. In addition, the dedicated A-D conversion circuit driving means 12
When is activated, the AD converter 2 is driven. The A / D conversion unit 2 performs A / D conversion of the input analog signal, and thereafter, when the internal A / D conversion value reading means 13 is driven, A / D conversion is performed.
The AD conversion value generated in the -D conversion unit 2 is read, and the read value is held in the holding unit 15. This operation is executed at regular intervals, and depending on the voltage value of the power supply of the processing device 1 or the required accuracy, only one of the internal A / D conversion unit 2 and the external dedicated A / D conversion circuit 3 is used. Is driven, and the other that is not driven is maintained in a stopped state without performing AD conversion operation.

FIG. 2 is a block diagram of an embodiment. In FIG. 2, 20 is a one-chip microcomputer (corresponding to the processing device 1 of FIG. 1), 21 is a data transfer control unit, 22 is an A-D conversion unit,
23 is a dedicated A-D conversion circuit (corresponding to 3 in FIG. 1), 24 is a data transfer control unit, 25 is an A-D conversion unit, 26 is a data control line, 27 is a battery, 28 is a level shift unit, 29
Is an AC adapter, 30 is a DC-DC converter, and 31 is a system circuit of a personal computer or the like that operates by the power supply from the battery 27 or the AC adapter. When the system circuit 31 can be connected to an AC power source, the AC power source is converted into a DC voltage by the AC adapter 29, converted into a voltage by the DC-DC converter 30, and supplied to the system circuit 31. When not connected to the AC power source, power is supplied from the battery 27 via the DC-DC converter 30. on the other hand,
When the AC power is supplied to the battery 27, DC-D
The charging voltage is supplied from the C converter 30 to perform charging, and the charging voltage (analog value) is changed to the A / D conversion unit 22 of the one-chip microcomputer 20 or the dedicated A / D conversion circuit 23.
This is detected by the A-D converter 25. When the operating voltage of the operation of the one-chip microcomputer is high, the voltage obtained by level-shifting the charging voltage of the battery 27 by the level shift unit 28 is detected by the AD converter 22 in the one-chip microcomputer 20. on the other hand,
When the operating voltage is low, A- of the dedicated AD conversion circuit 23
The D conversion unit 25 detects this. FIG. 3 is a processing flow of the one-chip microcomputer. This processing flow starts at a fixed cycle,
Repeated operation. First, it is judged whether high accuracy is required for A-D conversion (or whether the power supply of the one-chip microcomputer is low) (S1 in FIG. 3). If high accuracy is not required, a clock is supplied to the internal A / D conversion unit (22 in FIG. 2) to activate it (S2 in FIG. 3) and the internal A / D conversion port is selected (S3 in the same figure). ). Then, the operation of the internal A-D conversion unit starts (at step S4), and the internal A-D conversion operation starts (at step S5). Then, the conversion value of the internal AD conversion unit is read and the conversion value is stored in the memory (at step S6). Then inside A-
The operation to the D converter is stopped (at step S7). In S1 above, when high accuracy is required (or when the power supply of the one-chip microcomputer is high), the external AD converter (25 in FIG. 2)
To start supplying clocks to (S8 in FIG. 3). This activates the external A / D converter. Next, a specific port (port to which the charging voltage is input) is selected from the A-D conversion ports (assuming that there are a plurality of conversion ports) of the external A-D conversion unit (at step S9), and A-D is selected. Conversion starts (at step S10). Then, when the conversion operation is in progress (see S
11), the conversion value of the external A-D converter is read and stored in the memory (at step S12), and then the clock supply to the external A-D converter is stopped (at step S13). FIG. 4 is an explanatory diagram of data control lines and data transfer. A. of FIG. Shows the structure of the data control line (26 in FIG. 2), and B. Shows the waveform of command data, read data, and each signal. The data control line is provided between the data transfer control unit 21 of the one-chip microcomputer 20 and the data control unit 24 of the dedicated A / D conversion circuit 23, and a is a command for controlling the operation of the dedicated A / D conversion circuit. Is a line of A-D control command data for transmitting B. The data is sent serially as 8-bit data, as shown in. A. B is a serial clock line, and B. The clock signal with the waveform shown in
It is sent in synchronization with each bit of the D control command data, and is used by the dedicated A / D conversion circuit to receive the A / D control command data. A. C is a line of the serial data latch, and B. The waveform is as shown in (1), and when the A-D control command is transferred, one pulse is transferred from the one-chip microcomputer to the dedicated A-D conversion circuit and used to latch the command data. A. D is a line of A / D conversion value read data, and is a line of the dedicated A / D conversion circuit.
The A-D conversion value obtained by the -D conversion unit (25 in FIG. 2) is set to 1
It is a line that transfers serially to the chip microcomputer. This A
The D-converted value read data is B. As shown in, the read data consists of 8 bits. As shown in 1
It is transferred in synchronization with the serial clock from the chip microcomputer. A. E is the line of the clock for AD conversion,
This clock is sent to the dedicated A / D conversion circuit, so that the A / D conversion unit (2 in FIG. 2) in the dedicated A / D conversion circuit.
5) is driven to start the A-D conversion operation, and if the A-D conversion clock is not supplied, A of the dedicated A-D conversion circuit is
The -D conversion operation remains stopped. FIG. 5 is an explanatory view of the A-D conversion value read, and FIG. 6 shows a configuration example of the command and the conversion value. When it is desired to read the A / D converted value of the dedicated A / D conversion circuit, the A.D. A-
D control command on the data line a as shown in FIG.
A -D conversion start (A in Fig. 5) command is sent, and subsequently, A-D read dummy data (B in Fig. 5) is sent. In the A / D conversion start command, as shown in the configuration example in A of FIG. 6, a bit indicating the start of A / D conversion is set in MSB (most significant bit), and the following 3 bits are A-
The D port select is designated, and the lower 4 bits are all "0", whereby the A-D conversion start command code is displayed. FIG. 5B A-D lead (A-D
As for the dummy data for abbreviation of conversion value), as shown in the configuration example in FIG. 6B, the leading 4 bits are set to the dummy data, and the subsequent 4 bits are a code representing the dummy data for AD reading. Is set. This data is sent from the one-chip microcomputer at the time of reading the A-D converted value, and the A-D converted value is simultaneously read in parallel with this data.
C in FIG. 6 is read data of the A-D converted value shown in FIG. 5, and is composed of 8 bits AD0 to AD7. FIG. 7 is a diagram showing an A-D conversion table setting procedure. As shown in FIGS. 10 and 11, the A / D converted value changes depending on the operating voltage of the one-chip microcomputer. Explaining with an example, when the operating voltage of the one-chip microcomputer is 5V and the analog input voltage is 1V, the AD conversion value is the resolution of the one-chip microcomputer × 0.2. On the other hand, when the operating voltage of the 1-chip microcomputer is 4V and the analog input voltage is 1V, the AD conversion value is the resolution of the 1-chip microcomputer x.
25. In this way, when the operating voltage of the one-chip microcomputer changes, the A-D converted value also changes, so it is necessary to change the A-D converted value to be output corresponding to the operating voltage of the one-chip microcomputer. Therefore, it is necessary to set the A-D conversion table provided in the A-D conversion unit to generate the A-D converted value in correspondence with the operating voltage.
The setting operation for the -D conversion table is performed from the system circuit (31 in FIG. 2). As shown in FIG. 7, when setting data in the AD conversion table, the A-D conversion table setting command (a in FIG. 7) is first transferred, and the 1-chip microcomputer converts by receiving the command. The table setting is prepared, and assuming that there are a plurality of A / D conversion ports, an A / D port selection code (the same b) that specifies which of the A / D conversion ports the conversion table is for
Is sent, and the conversion table of a specific A / D conversion port is selected. Next, the A-D conversion reference comparison data (same as c) is transferred, the data representing the reference comparison value corresponding to the standard value of the A-D conversion value is transferred, each reference comparison data is transferred sequentially, and finally The A-D conversion table end code (same as d) is transferred to. The one-chip microcomputer that receives them sequentially sets the A-D conversion table of the corresponding A-D conversion port.

According to the present invention, when the operating voltage can be operated within a certain range and the operating voltage is low and the AD converting accuracy is poor in the one-chip microcomputer having the AD converting function,
A-D conversion is performed by switching the external A-D conversion circuit.
-D conversion accuracy can be improved. Further, when one of the A / D conversion unit in the one-chip microcomputer or the external A / D conversion circuit is used, the other is stopped to realize low power consumption.

[Brief description of drawings]

FIG. 1 is a principle configuration diagram of the present invention.

FIG. 2 is a configuration diagram of an embodiment.

FIG. 3 is a processing flow of a one-chip microcomputer.

FIG. 4 is an explanatory diagram of data control lines and data transfer.

FIG. 5 is an explanatory diagram of AD conversion value read.

FIG. 6 is a diagram showing a configuration example of a command and a conversion value.

FIG. 7 is a diagram showing an AD conversion table setting procedure.

FIG. 8 is a configuration diagram of a conventional AD conversion unit.

FIG. 9 is a diagram showing an example of charging characteristics of a secondary battery (for example, a NiCd battery).

FIG. 10 is a block configuration for detecting and controlling a state of charge of a battery.

FIG. 11 is an explanatory diagram of a problem.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Processing device 10 Request determination means 11 A-D conversion part drive means 12 Dedicated A-D conversion circuit drive means 13 Internal A-D conversion value reading means 14 Dedicated A-D conversion value reading means 15 Holding means 2 A-D conversion Part 3 Dedicated A-D conversion circuit 4 Signal line

Claims (3)

[Claims] 1. In an A-D conversion method in a processing device having an A-D conversion unit inside and capable of operating in a fixed range of operating voltage, a highly accurate dedicated A-D conversion circuit is provided outside the processing device. It is determined whether or not high precision is required for the A / D conversion in the processing device, and the internal A / D conversion unit is activated, or the external dedicated A / D conversion circuit is activated. A request discriminating means is provided, and when one of the corresponding internal AD converting section or external dedicated AD converting circuit is driven by the request discriminating means,
The other circuit which is not driven maintains the stopped state, which is an A-D conversion method. 2. The A / D conversion clock line for controlling at least an A / D conversion operation between the processing device and the external dedicated A / D conversion circuit, and the A / D conversion according to claim 1. Data line for transferring value data,
A command data line for transferring a command is provided, and the external dedicated A-D conversion circuit is driven or stopped by sending or stopping a clock from the processing device to the A-D conversion clock line. A-D conversion method. 3. The A / D conversion table for holding data serving as a reference for generating an A / D conversion value is provided in the A / D conversion unit inside the processing device according to claim 1 or 2, An A-D conversion method, wherein highly accurate A-D conversion values are generated in response to changes in operating voltage by externally setting data including a command in a conversion table.