IEEE Transactions on Magnetics

V.Rama Gowri .B., 2P.K.Suresh, 3Prof. M.Murali
M.Tech Scholar, BABA Institute of Technology & Sciences, Visakhapatnam, AP-India
Assisstanr Professor, ECE Dept, BABA Institute of Technology & Sciences, Visakhapatnam, AP-India
HOD, ECE Dept, BABA Institute of Technology & Sciences, Visakhapatnam, AP-India
transmission of serial & parallel data. UART is a serial
Abstract--A soft processor is configured from the logic
communication protocol which is extensively used for data
resources inside the FPGA. Soft cores are simpler (more
communication as it uses full duplex communication in
primitive) and slower than their hard-core counterparts.
However, they have the advantage that you only need to
serial link, which gives us advantages like use of less no. of
transmission lines, increased transmission distance, and
implement a core if you need it and that you can instantiate as
many cores as you require until you run out of resources in the
form of programmable logic blocks. A hard microprocessor
more reliability and also it reduces the distortions in a
core is implemented as a dedicated, predefined block. A hard
core processor does not provide the flexibility of modification
In electronic industry basically intellectual property(IP)
to suit the application. In addition, only specific FPGAs will
core is a reusable part, where it can be used alone or in
have the option of having a hard-core; therefore, the choice of
group. These can be basic building blocks of several chip
vendors and FPGAs are limited. MIPS (originally an acronym
designs or logic designs. These can be configured in two
for Microprocessor without Interlocked Pipeline Stages) is
a reduced instruction set computer (RISC) instruction set
architecture (ISA) developed by MIPS Technologies (formerly
MIPS Computer Systems, Inc.). The early MIPS architectures
ways such as soft cores and hard cores. As there is a
tremendous growth in embedded Systems with which the
complexity increase so the better idea is to use the
were 32-bit, with 64-bit versions added later. The number of
reconfigurable and reusable cores as these are technology
instructions executed by the MIPS is high and it fulfills the
need of real time applications. By observing all the above
applications[4][3]. The above can be obtained with the
constraints and available features our objective is to develop
advent use of soft cores. of course hard cores also often
peripherals and synthesize a verilog code for embedded
good predictability of chip performance but whose
processors which includes peripherals like programmable
application function cannot be modified fruitfully. So soft
cores are preferred because of their reusability.
communication at very low cost. In this paper the UART serial
communication controller is designed and tested thoroughly.
All the simulation and synthesis of these IP cores are carried
In UART design, for achieving the speed matching of the
out in XILINX 13.3 and implemented in FPGA development
processor and UART interface. It takes asynchronous First
In First Out (FIFO)s as buffers to realize data exchange
Index Terms-- FPGA; Soft cores; IP; UART.
between UART and external devices.[1].In the design of
high speed UART ,before synthesizing the overall design the
baud rate generator is incorporated into the UART
Serial port is responsible for its serial data transmission,
design[2].Field Programmable Gate Array(FPGAs) are
where a serial port is a global tool in a computer. This serial
increasingly used for implementing embedded systems. Soft
port is provided with UART, which manages the data
core processors for FPGAs are becoming popular due to
reduced design cost, flexibility.[6] Now a days ,embedded
processor cores are integrated into most system-on-chip
(SoC) applications. Reusing of generic processors is often
preferred due to time to time market constraints[4]. A soft
core processor is used for customizing a given application
and synthesized for a target. Soft core processors provide
several advantages like reduced cost, flexibility, platform
independence and great immunity to obsolescence. So soft
Fig. 1. Baud Rate Generator
cores are used for embedded applications[3]. A nonpipelined Reduced Instruction Set Computer (RISC)
The BAUD rate generator divides down the system clock to
processor is used for signal processing applications. These
provide the bit clock (Bclk) with a period equal to one bit
RISC processors are designed for executing Instruction set
time and also Bclk8, which has frequency eight times the
and it can be realized using VerilogHDL.[7] Because of
popular applications of IP cores, these are frequently used in
programmable transmits and receive bit timing device.
SOC applications.[5] In this paper, synthesizable IP cores of
Given the programmed value, it generates a periodic pulse,
low cost peripherals are used for embedded SoC
which determines the baud rate of the UART transmission.
applications. For that Verilog description language is used in
This pulse is used by the receiver and transmitter circuit to
order to pursuit & integrate soft cores with RISC processor.
generate a sampling pulse for sampling the received serial
In these soft cores, with the help of Verilog code by
data and to determine the bit width of the transmit data. The
dumping in any FPGA and whose operation can be verified
first process increments the divide-by-13 counter on the
and it can be further reprogrammed UART module includes
rising edge of the clock. The second process increments
three sub modules such as baud rate generator, transmitter
divide-by-256 counter on the rising edge of clkdiv13. A
module & receiver module. The following is the descriptions
concurrent statement generates the MUX(multiplexer)
regarding the modules mentioned above.
output, BclkX8. The third process increments the divide-by-
8 counter on the rising edge of BclkX8. UART includes
II. Description of UART
another part called transmitter. This is generally a shift
The baud rate is defined as the no. of distinct symbols
register that shifts it out bit by bit with a specific rate. UART
transmitted per second irrespective of form of encoding. A
transmitter fetches data in parallel format and instructs the
symbol is one of several voltage, frequency (or) phase
UART to transmit it in a serial format with respect to frame
changer. Before going to the synthesizing process the
format. This frame format generally includes start bit, stop
programmable baud rate generate must be included as a
bit, parity bit and ideal state.
major part with UART[2], which is primarily used for
dividing the system clock by accepting the clock input and
given bit clock (Bclk) whose frequency is 8 times the bclk
frequency. This periodic pulse is used for knowing the baud
rate of UART transmission. This generated pulse is further
Fig. 2. Serial data Transmission
useful for receiver control and transmitter control of UART,
to determine the bit width of the transmit data and also for
setting receiver based rate.
III. State Machine Charts
The transmission of data will be initiated by checking the
holding register (TXD hold reg) (Or FIFO) for the data. If it
holds the data, then the start bit will be included which is
responsible for alerting the receiver to receive the data to be
sent. Now, the data i.e. in the holding register is to be loaded
into the transmit register through the local bus and the
“Transmit data read “would set enable. This signal indicates
the starting of a sequence and a new value will be loaded.
To send the frame in bit by bit format the Baud rates of baud
rate generator and transmitter must be synchronized. After
synchronization Least Significant Bit (LSB) will be
transmitted first. After sending the data bit, the transmitter at
last sends the parity bit which is used by the receiver to
check the error if present in it. In order to escape from the
incorrectly formatted received data, transmitter must add at
least one stop bit. If the holding register holds another
symbol, the above process will be repeated; otherwise the
transmitter will jump into an ideal state.
The following occurs, when Micro Controller is ready.
The Micro controller will remain in ideal mode till TDRE
Fig. 3. SM Chart for Transmitter
(Transmit data register enable) = 1 and it loads data into
TDR and clears TDRE.The UART transmits data from TDR
Receiver: The receiver must be responsible for data
to TSR & sets TDRE.Eight data bits will be included by
transmission to receive data in serial format by ignoring start
stop bit (“0”) & Stop bit (“1”) Now, In the ideal state, State
bit and stop bit. A receiver has to generate a local clock in
waits till TDR is loaded and TDRE in
order to be synchronized with transmitter whenever the start
cleared.When TDRE is set State Machine checks for
bit is received. This is because of the Asynchronous
synchronization in SYNCH state when it gets raising edge
behavior of UART. Baud rates must by synchronized before
bit clock (Bclk) then LSB will be transmitted for one bit at a
transmitting or receiving the data. According to the baud
time. Now in TDATA state Bclk is checked and the TSR is
clock of the baud rate generator, receiver receives the data
shifted to
the next bit which is to be transmitted and
after detecting the start bit. It will be completed after the
simultaneously bit counter will be incremented. When Bct =
stop bit is received. In order to check the correctness of data
9, eight bit data including stop bit will be transmitted. After
parity bit is used. In case of invalid stop bit (or) error, the
successful transmission Bct will be cleared and SM reverts
frame error will be enabled. After receiving the data, “
back to its ideal mode.
Receiver data Write” in going to be set .The following will
be procedure for UART receiver to receive data
a) Once the start bit is reached from transmitter, it
detects the remaining bits serially and shifts them
into RSR
b) When all bits including stop bit is received,the RSR
will be loaded into RDR, & RDRF will be set.
c) The Micro Controller will check the RDRF flag, and
RDR is read and flag is cleared once it is checked.
SM will remain ideal till RXD is loaded. once it is set ‘0’
processor is realized using Verilog HDL for executing
start bit will be detected. If the bits in the RXD are not
instruction sets[7].
synchronized with local bit lock (Bclk), there may occur a
problem if RXD changed the clock edge. In order to
overcome the above problem each bit must be sampled eight
times, on the rising edge of bclk8.
Fig .5. Output Test-Bench of UART
The above shows the output waveform of UART. On the
transmitter side we have applied a input bit stream of
Figure 2. The whole diagram of the system
10101100.The corresponding output at receiver side is also
the same which can be read from the above diagram. With
the inclusion of the Baud Rate Generator with the delay of
We used verilog hard ware description language for
clock pulse ,the input appears at the receiver.
implementation. Hardware description languages are useful
in verifying FPGA circuits[2]. The HDL is also used to
develop the Register-Transfer Level(RTL) model of UART
protocol, which is used to test transmission and reception of
The significance of the IP cores and its application with
different data frames. And also test bench wave forms are
advantages is demonstrated using the design and synthesis of
generated for the above mentioned modules. Xilinx ISE 131
UART. This UART design is building block of entire soft
is used for synthesis of above mentioned IP cores. The
cores for the complete architecture of the processor. The
synthesizable soft cores of embedded peripherals are
results pertaining to the SM charts and the output wave
developed and are interfaced with the RISC processor to
forms for the corresponding inputs are mentioned in the
enhance the advantages such as low cost, reliability &
Figures presented in the results section.
compatibility. The characteristics of soft cores can also be
Reduced instruction set computer (RISC) architectures are
the basic building blocks of high performance processors.
RISC has a simplified instruction set, with register- to
register arithmetic instructions. Here memory only can be
accessed by load and store instructions Here we are going to
determine the importance of a reconfigurable processor core
(soft core) based on RISC architecture as initiative for
instructions could not be performed efficiently on 8 bit
processor here we prefer RISC processor. Here RISC
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