Automatic test equipment in military and industrial applications more and more widely, but the circuit unit especially Board test, because the measured unit types, number of channels being measured, traditional switch matrix switch bulky, slow, poor electrical performance.
Can not meet the modern high-speed, portable test instruments. This article describes a USB interface, using the I2C bus transfer data from CPLD multiplexer devices large switch matrix structure, with a high switching speed and good electrical properties, and meets the requirements miniaturization.2 system structure and function
Switch matrix main realization of automatic test equipment and test circuit for the exchange of information between units, functions as follows:
(1) the program-controlled power supply system output power automatically to be logging circuit unit required pin;
(2) the use of automatic test equipment signal source separation system output signal transfer to be logging circuit unit required pin;
(3) will be measuring circuit unit output signal transfer to automatically test the device on the appropriate channel;
(4) to be logging circuit unit to provide the necessary external components, such as load, adjustment knob, bulky devices, etc.
Different test circuit element as the definition of the connector, each pin can be defined as the power, input signal and output signal, one of the external component terminals.
And modern electronic equipment for circuit unit channels a lot, a lot of signal channel on the switch matrix design ATE presented a serious challenge. This article describes the design of the switch matrix take needle bed connections, which can effectively connect multiple connectors. By SCM multiplexers that can be applied to the desired test channel, system architecture diagram shown in Figure l.3 hardware design
3.1 test circuit structure
Test circuit structure as shown in Figure 2.
System uses the upper and lower computer architecture, computer controlled by the computer and software components, lower computer by the USB bus interface and dashboard, USB module via the I2C bus control data to the Control Panel on each test module. The control board all test modules receive bus sent serial code stream, and decoding the value after the extraction of addresses, control module for multiplexers (muxes) select the appropriate channel. I2C is a serial bus peripheral interface that uses synchronous mode serial receive or send information, master-slave device on the same clock, I2C by cable SDA and SCL clock line constitutes a bidirectional I2C serial bus, because only one data line, so the information sent and received only timesharing. The modular components are connected in parallel on the bus, each module has a unique address. So the system can allow the scope to increase or decrease the number of test panels, I2C bus on the node module supports hot-plug, so take it can effectively reduce the testing system volume, use the convenient operation, you can simultaneously connect to multiple units being measured.
3.2 control circuit
This system, the control board all test modules through an I2C bus to communicate with the test host, the module address by on-board I2C chip address only, the host first determine your card address Board elections, and the Board to establish communication, SDA serial control data sent.
At the same time, the I2C bus on only one module is active, use the multiplexer status of "keep" feature, you can implement the test module and test probes for switching between modules. Control panel circuit structure as shown in Figure 3.PCA9501 is a band break 8-bit I2C-bus and SMBus devices for receiving and sending data bus and a local address, if the same result as you convert data into parallel address signals sent to the CPLD EMP7128, CPLD to receive PCA9501 send parallel data, and analyze data, different serial data converted to the corresponding parallel control data and sent through the I/O port to control 32 channel multiplexer devices ADG732 channel selection.
4 system software design
System software including host controls and slave test program, host control can use a general programming tools such as VisualC + + or C ++ Builder, etc. to be written.
Slave test program including USB control program, sending program, CPLD I2C control programs, including USB control program and send program is I2C USB controller to program, using CY7C68013 Keil C51 compiler development, CPLD control program uses MAX P L U S Ⅱ, Verilog HDL hardware description language.4.1 host control program design
Host control program design depends on the slave control processes, lower computer control process as shown in Figure 4.
(1) open the USB device and initialized, and then reset the device, all the internal switch open ADD732 chip.
(2) host a release command to be logging plate selection, test panels address consists of the measured onboard PCA9501 determine, under test plates to select only need to send data to the desired address, all measured Board received address data only through comparison of the measured panels will be by PCA9501 data is sent to the CPLD.
(3) select the measured sheet, select the test chip that multiplexer array multiplexed device choice, CPLD parse the received data, a chip select the data transformation in pairs multiplexer slice selected signal, and disable the multiplexer devices.
(4) host programs will be test point addresses sent to US
B endpoint buffer, by sending endpoint CPLD analysis to select the data, the data conversion pairs multiplexer channels select signal, and enabling the multiplexer devices, the Board selected, sheet elections and test point selection data sent out at the same time, the corresponding test panel multiplexer will breakover, enabling the selection of the test points.(5) each chip all point test has been completed, the next chip test before, you will need to reset the chip.
Similarly in all test points, test is complete, reset the entire switch matrix.Your location: Home > > body simulation design
Technology category: analog design
Foreign electronic components | Author: Wang Sheng Liu Yao Liu Huan shines week
Master program data send part of the program are as follows:
4.2 slave test program design
Slave test program including USB microcontroller CY7C68013 receive host send control data, and interpretation of the host data, and then by the single chip I2C interface to data sent to the test Board I2C data converter pieces PCA9501, PCA9501 will receive the test plate address is compared with its own address, such as the same automatically serial data into parallel data sent CPLD, CPLD resolution parallel data sent, and then enable signal effect (through USB controller parts CY7C68013 of PB7) data to be sent out at the same time.
SCM receives/sends data to the program are as follows:
CPLD to receive PCA9501 parallel data sent and received data are interpreted, and then convert it into pairs multiplexer devices of the control signal, ADG732 procedures are as follows:
5. concluding remarks
This system uses the USB interface and I2C data transmission, effectively reducing the system volume, for multi-channel switch matrix made of small useful explorations.
The development of switch matrices can hook several test modules, and supports hot-plug, with strong versatility and scalability, and traditional fixed test compared to the needle bed, without the need for each test circuit board manufacture specialized channel plates, reduces the volume and lowers costs for low-cost, portable, generalization, multi-channel testing scenarios provides a new means of implementation.
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