Author Email: zcyhero@yeah.net
Abstract: This article introduces under the TMS320VC33 control in detail the earthquake recording instrument’s overall design process. This system is uses TMS320VC33 is master control chip gathering transforms after 16 a/d conversion chip AD976 16 digital quantity; Completes after the TMS320VC33 processing 16 digital quantity with the superior computer correspondence. Mainly has applied the sampling technique, the filter technique, the digital filtering technology, the DSP technology, modern circuit design technologies and so on digital signal processing technology, causes this system to become the data acquisition the fine standard product.
Key word: DSP (digital signal processing), sampling, filter, a/d conversion (A/D)
Introduction
This design mainly uses 32 floating point digital signal processing chip TMS320VC33 which TI Corporation produces to take system’s master control chip; Uses 16 a/d conversion chip AD976 which Analog Corporation produces to take a/d conversion chip; Uses eight step switch electric capacity type low pass filter LTC1064-2 which Linear Corporation produces to take the hardware filter chip. This system function realizes mainly divides into two parts namely: Hardware circuit design and DSP software routine design.
1. Hardware circuit design
Considered the system function realization, the hardware circuit design mainly divides into four parts namely: The signal pre-processing and signal filtering processing, signal AD transforms, the DSP function to realize, computer interface circuit. System diagram like chart 1:
1.1 signal pre-processings and filter processing
Before the signal, buyer, if through DG419ER chooses an analog switch to carry on the cut selection to two measuring range signals, the DG419 control origin DSP positive governing, the simulated signal gives the LF356 operational amplifier through DG419, the clear signal enlargement and the first-level filter. Here artificial has made second-order filter with the operational amplifier, signal shaping processing peak-to-peak value for ±10V the preparation supplies AD the voltage signal. Carries on the choice through pre-processing’s simulated signal after DG419 to divide into two kind of situations by the DSP control namely or gives AD976 directly through the LTC1064-2 filter channel, through LTC1064-2 advance signal’s high frequency elimination, filter’s corner frequency the filter clock controlling which provides by DSP.
1.2 a/ds conversion
The signal ±10V the voltage signal delivers modulus switch AD976 after the pretage reshaping and the filter, a simulation quantity transforms after AD has 16 digital voltage quantity, after the transformation had ended saves the pulse by the AD976 BUSY base pin’s condition for the following 74HC574yi lock, saves 16 digital quantity signal lock to 74HC574 on, waited for that DSP reads the data. Inside the AD976 transformation and the pretage DG419 signal selection is by DSP master control, after the time can guarantee that reads AD transforms the valid data.
1.3 DSP functions realize
TMS320VC33 is the high performance floating point digital signal processing chip which TI Corporation produces, needs to consider several aspects according to the DSP chip’s characteristic:
(1) power supply
DSP itself uses the 3.3V working voltage, uses 1.8V to lock to the link voltage, needs to use power source chip TPS767D318 which TI Corporation recommends the 5V supply voltage to transform 3.3V and 1.8V.
(2) crystal oscillator produces the electric circuit
The crystal vibration starting of oscillation resistance which and the electric capacity uses differently according to the use crystal oscillator are different, here uses the 10M crystal oscillator, the starting of oscillation resistance and the electric capacity selects 470 ohms and the 15pF electric capacities separately.
(3) locks to the link electric circuit
Locks needs to use to the link recommends the electric circuit, the resistance which the attention uses respectively is 100 ohms and 103 electric capacities.
(4) level switch electric circuit
Because DSPVC33 can only accept the 3.3V level signal, therefore needs to use level switch chip 74LVT245 to carry on the level switch, simultaneously considers to the 74LVT245 read-write logical operation.
1.4 computer interface circuit design
Computation interface circuit diagram as shown in Figure 2.
The computer interface circuit mainly completes the computer and the DSP correspondence function. The computer through gives a DSP hardware interrupt to the DSP transmission data, when after DSP response hardware interrupt, through procedure interrupt clear. The computer judges the FIFO condition through the logical control data, decided that reads the FIFO data the time. Like this has completed DSP and the superior computer’s connection.
2. DSP software routine design
The DSP software routine design mainly completes the transmission port select sampling clock, the filter clock; Gathers the AD data; Processes the AD data (including digital filtering and data ordering); Preserved data to the FIFO memory; Processing hardware interrupt. DSP software routine flow chart like chart 3, chart 4, shown in Figure 5.
3. Conclusion
The DSP control’s data acquisition system has mainly applied the modern electronic circuit design method, the digital signal processing technology, the simulation filter technique, the system antijamming technology, the hypothesized instrument technology, the programmable logical control technology. The overall system has selected one batch of high performance chip, guarantee system’s reliability and system’s gathering precision, is the data acquisition fine standard product.
