To design a UART which is implemented with Verilog HDL can be easily integrated VHDL implementation of UART with BIST capability. This paper focuses on the design of a UART chip with embedded BIST .. Yaacob, Zaidi Razak, “A VHDL Implementation Of UART Design with BIST capability”. Designed is implemented in Verilog HDL and . VHDL Implementation of UART Design with BIST. Capability protocol (where data is sent one bit at a time).

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Published on Dec View 5 Download 5. Malaysian Journal of Computer Science, Vol. Design and test engineers have no choice but to accept new responsibilities that had been performed by groups of technicians in the previous years.

Design engineers who do not design systems with full testability in mind open themselves to the increased possibility of product failures and missed market opportunities. BIST is a design technique that allows a circuit to test itself. In this paper, the test performance achieved with the implementation of BIST is proven to be adequate to offset the disincentive of the hardware overhead produced by the additional BIST circuit. The technique can provide shorter test time compared to an externally applied test and allows the use of low-cost test equipment during all stages of production.

Although BIST techniques are becoming more common in industry, the additional BIST circuit that increases the hardware overhead increases design time and performance degradation is often cited as the reason for the limited use of BIST [1]. In the implementation phase, the BIST technique will be incorporated into the UART design before the overall design is synthesized by means of reconfiguring the existing design to match testability requirements. In circuit testing, another traditional test method works by physically accessing each wire on the board via costly bed of nails probes and testers.

To identify reliable testing methods which will reduce the cost of test equipment, a research to verify each VLSI testing problems has been conducted. The major problems detected so far are as follows: The numbers of test patterns are becoming too large to be handled by an external tester and this has resulted in high computation costs and has outstripped reasonable available time for production testing.

Another test generation problem is that computer algorithms providing Automatic Test Pattern Generation ATPG work well for combinatorial logic but rather poorly for sequential logic circuits. Sequential circuits demand too much computer memory and computation since many more time states must be evaluated [2a].

This is the number of test vectors required to exhaustively test a circuit for those functions that a customer might use. However, a finite number of test vectors can still be applied to an IC and follow the economic rules of production.

The finite number of test vectors is much lesser than the full exhaustive test set of a VLSI circuit [2a]. This makes testing of internal nodes more difficult as they could neither no longer be easily controlled by signal from an input pin controllability nor easily observed at an output pin observe ability.

Pin counts go at a much slower rate than gate counts, which worsens the controllability and observe ability of internal gate nodes [2a]. The VLSI testing problems described above have motivated designers to identify reliable test methods in solving these difficulties. An insertion of special test circuitry on the VLSI circuit that allows efficient test coverage is the answer to the matter.

The need for the insertion has been addressed by the need for design for testability and hence the need for BIST.


The review inevitably occurred late in the design cycle; adversely affecting project schedules if glitches were found, and making for an uncomfortable process for the circuit designer. However, with today’s design practices, schematics are mostly outdated [3]. Nevertheless, finding DFT problems in language-based designs is still not a simple task for humans. The acceptance of the design for test techniques has been largely due to the possibility of Verilog support to this design style.

The high degree of standardization makes it possible to have most wwith feature previously added to a design using Verilog [4] [5].

A serial port is one of the most universal parts of a computer. It is a connector where serial line is attached and connected to peripheral devices such as mouse, modem, printer and even desitn another computer.

The serial port is usually connected to UART, an integrated circuit which handles the conversion between serial and parallel data [6] [7]. To transfer data on a telephone line, the data must be converted from 0s and 1s to audio tones or sounds the audio tones are sinusoidal bbist signals. The modem takes the signal on the single wire and converts it to sounds. Capabioity the other end, the modem converts the sound back to voltages, and another UART converts the stream of 0s and 1s back to bytes of parallel data.

Serial Data Transmission and Receive 5. The UART are capable of the following [8]: Loopback controls for communications link fault isolation Break, parity, overrun, and framing error simulation BIST Table 1: CS is an active low signal latches address strobe for completing chip selection. Ri IN Ring Indicator When low indicates that the telephone ringing signal has been received by the modem or data set Dcd IN Data Carrier Detect When low indicates that the modem or capabilit set has detected a data carrier.

Data, control words and status information are transferred via the data bus. For each implementatiob of the flip-flops and for each input combination, the network outputs need to be verified. One approach would be to connect the output of each flip-flop within the IC being tested to one of the IC pins.

Since the number of pins on the IC is limited, this approach is not practical. The solution to the question is by arranging flip-flops to form a shift register.

The state of the flip-flop will be shifted out bit-by-bit using a single serial-output pin on the IC. This is called dexign path testing [9] [10]. BILBO is a scan register that can be modified to serve as a state register, a pattern generator, a signature register, or a shift register.

XOR force 01 to Deign parallel data is then fed to the UARTs transmitter. The UART converts the pseudo random parallel data to serial data which is then looped back to its receiver to create an internal diagnostic capability. Following the scan, it is compared vsrilog the correct signature biist from the simulation of the entire self-test sequence approach in a tester.

The transmitter and receiver simulation under normal mode is presented next followed by the simulation of UART under testing mode in succeeding section.

A Verilog Implementation of Uart Design With Bist Capability

The transmission was set at The 3-bit high data is equal to Therefore 1 data bit is equal to Serial 8-bits data transmission at TXD 7. The output of the received parallel data is then routed to DATA[7: This mode is used to test both the transmitter and receiver of the UART.

The mode will loop-back the serial data and transmit the data back to the receiver. These parallel signals are then converted to serial data in a communication line and will be looped back to the receiver. The produced signature is then compared with the correct signature. The other remaining bits b6b0 are shifted to the left.


Therefore, there should be a method to send out the signature without sacrificing extra observance output pins. The signature is shifted out at serial data out so outputs pin. As can be observed, so is transmitted as the following sequence: The signature produced is also similar with the correct signature achieved from the simulation of the entire self-test sequence approach using C programming.

The RTL schematic is shown in Fig. Therefore, there is a need to verify the design implementation on a real hardware. The test is admittedly lacking of tact or taste but will serve if access to better equipment is not possible. It will be used to force logic levels onto the input pins of the FPGA to test a downloaded logic circuit. For further test, the LFSR can be initialized by changing the si states using a programmable signal generator and its appropriate software.

The result of the pseudo random pattern generator PRPG waveforms can be observed using oscilloscope or logic analyzer. The left most data on Fig.

LSB followed by The waveforms obtained have proven the result of 8-bits PRPG in simulation and theory. The other remaining bits b6b0 are then shifted to the left. Therefore, the result will be How the LSB is achieved is shown below: Pseudo random pattern 8. These data act as the data output of the circuit under test. The MISR outputs are then observed at outputs q using mixed signal oscilloscope.

The left most data the dotted line is observed as followed by How the caapability result is produced is shown below: However, as stated before, the reasons for the limited use of BIST are due to area overhead, performance degradation and increased design time. In this section, the reports after the optimization process will be used as a basis for comparing the UART design capabilit and after the implementation of the BIST technique.

By comparing these reports, it can be shown that the reliability of the chosen technique for the testable UART chip can be proven. The implementation of BIST technique has also resulted in the decrease of the maximum frequency from The reason why the design may not cater for high-speed clock is due to the possibility of a real time delay, which may be caused by temperature or the delay within the FPGA design itself e.

The delay will limit the capability of data to be captured at some critical point.

Verilog Uart .pdf

The faulty data captured may lead to errors at the output pins. The simulated waveforms also have shown the observer how long the test result can be achieved by using the BIST technique. The test as shown earlier in Fig. This is the most important thing that should not be left out by any designer to ensure the reliability of their design. In spite of the hardware overhead obtained with BIST implementation, the overhead is somehow reasonable considering the test performance obtained.

The research has proven that implementing BIST in a design has effectively satisfied on-chip test generation and evaluation. With the implementation of BIST, expensive tester requirements and testing procedures starting from circuit or logic level to field level testing are minimized. The reduction of the test cost will lead to the reduction of overall production cost. Design summary Design Summary: Total equivalent gate count for design: