“MIL-STD-1553 was issued by the US Department of Defense in 1973 as a military serial bus standard. This standard defines the mechanical, electrical and functional characteristics of the bus. The 1553 bus was first used in aviation equipment, and later also widely used in aerospace data management systems. As a command/response half-duplex serial bus, it uses dual redundant balanced transmission lines (shielded twisted pair), and can connect up to 31 terminal (RT) devices through time division multiplexing.Due to the use of Manchester encoding, MIL-STD-1553 bus data can be transmitted in a transformer-isolated transmission line, which can be
MIL-STD-1553 was issued by the US Department of Defense in 1973 as a military serial bus standard. This standard defines the mechanical, electrical and functional characteristics of the bus. The 1553 bus was first used in aviation equipment, and later also widely used in aerospace data management systems. As a command/response half-duplex serial bus, it uses dual redundant balanced transmission lines (shielded twisted pair), and can connect up to 31 terminal (RT) devices through time division multiplexing. Due to the Manchester encoding, MIL-STD-1553 bus data can be transmitted in a transformer-isolated transmission line, which can isolate the device node from the bus system, thereby improving the reliability of the bus system.
In view of the special bus structure and harsh application environment, perfect bus testing methods are undoubtedly the key to guarantee the reliability of the MIL-STD-1553 bus system. The current 1553 bus test is mostly based on MIL-HDBK-1553. The test standard covers a wide range of electrical performance tests and protocol tests. If the bus device can pass all the necessary item tests specified by the standard, this terminal The reliability of the equipment has been fundamentally guaranteed. But MIL-HDBK-1553 has higher requirements for test equipment. A comprehensive MIL-STD-1553 bus test equipment needs to have oscilloscope function, signal generator function and impedance measurement function at the same time. The key is to have fault injection function. The function of 1553 bus emulation terminal. At present, most of the test equipment/instruments that can be found on the market are single-function test equipment/instruments, such as independent oscilloscopes, independent signal generators, and independent 1553 bus emulation cards. If these independent devices are used to build a bus test system, the resulting test system will be very inconvenient to use, not only causing low test efficiency, but also too much manual intervention, resulting in inaccurate test results. In addition, the current bus simulation cards on the market can only inject some of the faults specified by MIL-HDBK-1553, and cannot achieve all the fault injection functions specified by the standard. This will greatly reduce the test coverage rate and often be buried in the bus equipment. Under the hidden dangers.
AT15000 is a multifunctional bus analyzer developed by Zhuhai Silicon Microelectronics Technology Co., Ltd. It integrates the functions of oscilloscope, signal generator, impedance tester, time domain reflectometer and 1553 bus emulation card. These device functions are organically combined in AT15000, Working together, it can realize all protocol tests and electrical performance tests specified by MIL-HDBK-1553, with high test coverage, which greatly reduces the difficulty of 1553 bus test equipment. As an ATE, most of the tests of AT15000 can be performed automatically. Users only need to perform a few manual interventions to complete a very complete test process. At the same time, AT15000 can also automatically generate tests in text format for product filing and testing. Tracking greatly improves test efficiency and test quality.
AT15000 divides the test into three parts according to different terminal types: BC test, BM test and RT test. According to the test standard, the electrical performance test and protocol test are divided into many test sub-items, which can be selected by the user through the test script. Testing the sub-projects and defining the test sequence makes the testing work very flexible and easy to control.
1. Terminal electrical performance test
The electrical performance test of the terminal includes input electrical performance test and output electrical performance test. A reliable terminal device must have good input signal tolerance and complete signal output characteristics.
Output characteristics include the amplitude of the output signal, zero-crossing stability, overshoot, ringing, rise/fall time, output symmetry, output noise, output isolation of the two channels, and switching noise of the power supply. In these types of performance tests, in addition to the zero-crossing stability test, the other types of tests require the cooperation of the oscilloscope module. AT15000 uses hardware logic to measure the zero-crossing stability of the signal on the bus in real time, and calculate the zero-crossing deviation of each bus word.
When the encoder encodes normally, the output zero-crossing stability is related to the system clock stability. If the system clock drifts a lot, it will also cause a larger zero-crossing deviation, which will result in abnormal data reception at the receiving end.
When the bus impedance is correctly matched, overshoot and ringing are mainly caused by the bus transmitter in the device under test. If the power supply design of the device under test is unreasonable, and the power supply to the transmitter is insufficient, overshoot and ringing will often occur on the bus.
The output symmetry is used to examine whether the output of the transmitter and the isolation transformer are symmetrical. In an ideal state, when the transmitter does not send a signal, the differential level on the bus should be 0 volts, but when the output of the device under test is asymmetric At the moment when the signal is sent, there will be a residual level on the bus. The standard stipulates that this residual level needs to be maintained within a value, otherwise the output symmetry of the bus device will be unqualified.
An ideal 1553 bus device should have small power switch noise and output noise, so that it will not affect the normal operation of other devices on the bus.
The standard stipulates that 1553 bus devices need to have two well-isolated channels that are mutually backup. If the isolation between these two channels is not enough, one of the channels will interfere with the signal on the other channel, thereby reducing the reliability of the bus.
Input characteristics include zero-crossing stability, acceptable signal amplitude, input impedance, common-mode rejection, and rise/fall time. Among these types of input characteristics, the zero-crossing stability test requires the cooperation of the 1553 bus controller fault injection logic to inject the response zero-crossing deviation in the sent bus word according to the needs of the test. The input impedance test requires the signal generator to inject an excitation sine wave, and the response signal is sampled through the oscilloscope module, and the input impedance of the device under test is calculated according to the true effective value of the excitation signal and the response signal.
The zero-crossing stability is used to test the decoding capability of the Manchester decoder and the stability of the terminal equipment clock. If the clock of the device is unstable, even if the decoder has a very good decoding capability, it will cause reception errors.
The received signal amplitude specified by the standard is between 0.28~27V. When the amplitude of the bus signal is within this range, the decoder of the device must correctly decode the bus data.
If the input impedance of the bus device is too low, it tends to increase the load of the bus, thereby reducing the amplitude of the bus signal and shortening the life of other bus devices.
The common-mode rejection capability is used to investigate the isolation of the isolation transformer of the bus terminal equipment. Under normal circumstances, the common mode noise on the secondary coil of the transformer will not affect the differential signal on the primary coil, otherwise the common mode noise will superimpose an interference on the differential signal received by the primary coil, thereby affecting the signal reception of the terminal equipment .
AT15000 adopts a fully automatic method to measure electrical characteristics, and its built-in oscilloscope module will automatically capture the bus signal that needs to be measured and calculate the corresponding characteristic parameters. No manual intervention is required during the testing process, and users only need to add the items to be tested in their test scripts. For BC and RT tests, after each test item is completed, AT15000 will automatically write the test results into the test, which provides great convenience for the test.
2. Protocol testing
The protocol test specified by the standard is divided into two parts: conventional test and fault injection. The conventional test requires that the BC/RT can receive/send the commands specified by the MIL-STD-1553B bus, the BM can correctly parse the bus protocol, and the fault injection requires the tester to be able to Inject various faults specified by the standard on the bus. When carrying out the protocol test, the conventional protocol test must be completed first, otherwise the fault injection test cannot be completed.
In order to meet the requirements of test standards, a bus test ATE must not only have the functions of an emulator, signal generator, and bus emulation terminal, but also the following functions specified by MIL-HDBK-1553:
Able to inject a zero-crossing deviation of not less than 250ns;
Ability to inject parity errors on any bus word;
Ability to inject arbitrary message length errors on different messages;
Ability to inject any length of word length error on any bus word;
It can inject phase encoding errors on any bit of the bus word, and can output high or low levels on the error bit;
Ability to inject data continuous errors on the bus;
Ability to inject replacement commands on the bus;
The response time of RT is adjustable from 0 microseconds to 14 microseconds;
RT can use any address to answer the bus command;
The RT response can be turned off by software (data must be received normally);
It is possible to inject 5 types of sync header errors specified by the standard on any bus word;
Able to generate bus switching commands;
Able to correctly identify all mode commands specified in the protocol;
It can inject white Gaussian noise with a root mean square of 140mv (200mv for direct coupling) and a frequency range of 1K to 4Mhz on the bus.
If the common MIL-STD-1553 bus control chip on the market is used, the above-mentioned bus fault injection function cannot be realized, and there is no commercial bus control chip with fault injection function for sale. So in order to realize the above-mentioned functions, test equipment developers need to develop 1553 bus control chip with fault injection function by themselves.
Based on the above considerations, Silicon Micro has independently developed a 1553 bus control IP core dedicated to bus test equipment, which can be implemented in multiple series of FPGAs of ACTEL and ALTERA. It is used to inject faults in a hard logic manner, so the IP core can be changed to achieve all fault injection functions specified by the standard. The functional block diagram of this IP core is shown in Table 1:
AT15000 multi-function bus analyzer can improve test efficiency and test quality
As shown in Table 1, one BC, one BM, and two multifunctional RTs are implemented in the controller IP core. These functions can work at the same time and can simulate 32 RTs at the same time. The IP core uses a 64M clock, which can inject zero-crossing deviation on the bus with a resolution of 15.6ns, which greatly improves the performance of the bus test. The verification of several types of bus test equipment by Silicon Micro has proved that the design of this IP core is reasonable and the working condition is stable and reliable.
If only the IP core of the 1553 controller is realized, the automatic test of the bus cannot be realized. In addition to the bus controller, the sampling logic of the oscilloscope, the logic of the signal generator and the logic of the time domain reflectometer must also be implemented. At the same time, these logics should be combined according to the requirements of the bus test standard to facilitate the test of the electrical performance of the bus. AT15000 adopts CYCLONEIII FPGA chip of ALTERA Company, realizes the above-mentioned several kinds of logics in FPGA. The oscilloscope logic can be triggered by the logic of the 1553 controller, making the test of the electrical characteristics of the bus very simple.
As an ATE, the bus test equipment needs to have a high degree of automation and minimize manual intervention. Therefore, when designing the tester software, it is necessary to carefully analyze the test standards, classify and refine the test items into several sub-test items, so that users can freely select test items and define the test sequence, so as to make the test more flexible and meet different test occasions. Needs. AT15000 divides the test into RT test, BM test and BC test according to the type of bus terminal equipment. At the same time, each test is divided into many sub-test items. Users can freely select test items and define the test sequence in the form of scripts. Among the three types of tests, in addition to the RT test, the BM and BC tests require the software of the tested device to cooperate, so when testing BM and BC, the user needs to write the software of the tested device to cooperate with the test Instrument test.
Since BM only has the function of bus monitoring, the tester has no way of knowing the current protocol reception status of BM. AT15000 according to the user’s script configuration, in accordance with the test standards, sends the response bus messages to the bus in turn, and after the message is sent, writes the sent bus messages to the test. After the test is completed, the user needs to export the messages received by the device under test to the PC. The host computer software “TESTMASTER” of AT15000 will analyze whether the BM test result is correct according to the two tests.
Before testing the BC, the user needs to write the BC test program according to the BC test manual of the AT15000 to cooperate with the test of the AT15000. In addition, AT15000 does not make judgments on the test results. The device under test needs to judge the test results by itself and send the test results to AT15000 via the bus.
For the RT test, AT15000 adopts a fully automatic method. While sending the corresponding test data, it will also judge whether the test result is correct or not. The user only needs to select the required test items in the test script, define the test sequence, and give the parameters of the tested RT required by AT15000 (such as RT address, RT legal receiving command, legal sending command, etc.). Can.
In view of the harsh application of MIL-STD-1553 bus, the test of 1553 bus equipment must also be detailed, so as to ensure the reliable operation of the bus system. Any negligence and sloppyness in the test will lead to serious consequences.
After the pioneers continue to summarize and summarize, the test standards of the 1553 bus are becoming increasingly strict, and it also brings challenges to the development of test equipment. The development of test equipment that meets the test standards is the prerequisite for 1553 bus testing. Good test equipment can not only improve the test efficiency of the bus, but also provide a strong guarantee for the reliability of the bus equipment.