By: Marganit Fina Supervisor: Rivkin Ina Winter 2007/8 Duration: Semester

Extended Uart The High Speed Digital Systems Laboratory,

Electrical Engineering Faculty, Technion

By: Marganit Fina

Supervisor: Rivkin Ina

Winter 2007/8

Duration: Semester

Final Presentation

Project purpose

Extending the UART IP Core from previous project ,to UART 16550 and adding additional features.

Goal : – Write a UART Core in VHDL, that can be used in other

projects– Synthesize the UART-Core for FPGA.– Two phases core-verification:

RTL logic verification ( VHDL-based test-benches) Lab – real-time testing of the core

UART work environment

PC

FPGA

RS-232communication

UARTCore

User

The UART passes bidirectional data from the PC to the User .

The USER uses the “services” of the UART to receive and send data from/to the PC.

Introduction : UART - Universal Asynchronous Receiver-Transmitter

Converts the bytes it receives from the computer along parallel circuits into a single serial bit stream for outbound transmission .

On inbound transmission, converts the serial bit stream into the bytes that the computer handles.

Adds a parity bit on outbound transmissions and checks the parity of incoming bytes and discards the parity bit (optional).

Adds start and stop delineators on outbound and strips them from inbound transmissions .

UART’s Features

Support sending and receiving data-packets in length of 5-8 bits.

– The UART has a new control interface ,which enable the client to determine the amount of bits (in a signal transaction).

Preamble data-assertion : the UART can add/remove standard asynchronous communication bits( start, stop and parity) for each received data-packet in the host-side.

– For all packet-lengths

UART’s Features - continue

Support even, odd and no-parity bit generation and detection.– Additional control interface to support parity

detection and generation, while sending the data in RS232.

Support sending 1,2 stop-bit.– The RS232 serial interface supports 1 or 2 stop

bits to signal the PC end of transaction.– The amount of stop bits is determined by the host.


Adding 16 byte send and receive buffers.– On the serial side of the UART (RS232) :

A 16 byte FIFO buffer , which enables store-and-forward received packets (to the Host).

– On the parallel side of the UART (Host) : A 16 byte FIFO buffer ,which store-and-forward the data

the host wants to send to the serial-side.


FIFO operation mode:– Using the UART I/F we can choose to use the FIFO support

or to work in 8250 Mode (without FIFO). In 8250 work-mode:

– Holding and shift registers eliminate the need for precise synchronization between the user and the serial data.

Interrupt/Polled mode operation:– Using the UART I/F we can choose whether to work in a

polled mode operation or in an interrupt mode operation. In both operations we can work with the FIFO support or without.


Programmable baud generator divides any input clock by to and generates the 16xClock.

Support baud rate from 2400 up-to 115200. Packet Checker logic

– When a new packet is collected. It detects parity error ,frame error or overrun error ,and reports it to the user on the Host side.

1 162 1

UART’s data-path example : User -> RS-232

UART’s data-path example : RS-232 -> User

UART- Top view

UART Port-Map: User’s Interface side

OUTPUTS – to the user:OUTPUTS – to the user:– IntRx_N

in 8250 mode: informs about a new data that has arrived. in FIFO mode: informs that the received FIFO (RCVR) has

reached the trigger level ,that was set by the user.– IntTx_N

in 8250 mode: informs that the transmit unit (TxUnit) is ready to send a new data.

in FIFO mode: informs that the transmitted FIFO (XMIT) isn’t full, therefore the user can load another new data to the UART.


OUTPUTS – to the user :OUTPUTS – to the user :– Ferr_N

indicates about a frame error (interrupt mode only).– Oerr_N

Indicates about an overrun error (interrupt mode only).– Paerr

indicates about a parity error (interrupt mode only).– SysClk

the transmit unit clock.– DataOut

from here we get the new 8,7,6 or 5 -bit data (parallel form).


OUTPUTS – to the user :OUTPUTS – to the user :– Empty_xmit

indicates that the UART has sent all the data that was given to him by the user (FIFO and interrupt mode only).

– RCVR_empty indicates that there is no new data for the user to read. (FIFO and

interrupt mode only).


OUTPUTS – to the user :OUTPUTS – to the user :– Status [7:0]

operates in polled mode in both 8250 and FIFO operations .gives information about the status of the UART:

– Full/Emptiness of the FIFO’s , Transmit and Receive Units.– Overrun error.– Parity error .– Frame error.


INPUTS to the UART:INPUTS to the UART:– FPGA_Clk

• FPGA base clock.

– Divider • Determining the Baud Rate.

– Reset• Active-low

– Mode• Determining whether use fifo support or not.

– Int_enable• Determining interrupt or polled mode operation.

– CS_Write• Loading a new data to the UART for transmitting.


• INPUTS to the UART:INPUTS to the UART:– Length

determining the data length ( 5,6,7 or 8 bits)– Parity

determining if we work with odd, even or non parity bit.– Stop

determining the amount of stop-bit we are working with (1,2 stop-bit).– Cs_status

for reading the uart status in polled mode.– St_n

for reading the uart status in polled mode.– RCVR_Trigger

in fifo mode , this input is used to set the trigger level of the received fifo’s interrupt.(1,4,8 or 14 bytes)

UART I/F : The Host’s side I/F

INPUTS to the UART: INPUTS to the UART: – Wr_n

• Loading a new data to the uart for transmitting.– CS_Read

Reading the new received data.– Rd_n

Reading the new received data.

– DataIn The parallel 8,7,6 or 5-bit data-input, which the UART will send to the

Serial-side.

UART Port-Map: RS-232 I/F

INPUTS to the UART:INPUTS to the UART:– RxD - the received data line – (pin #2) – CTS - Clear To Send (pin #8)- always at low.– DSR- Data Set Ready (pin #6) - always at low.– GND- Ground (pin #5)– DCD – Data Carrier Detect (pin #1) – always at low.– RI – Ring Indicator (pin #9)-always at high.

UART Port-Map: RS-232 I/F

OUTPUTS from the UART:OUTPUTS from the UART:– TxD -the transmitted data line- (pin #3)– RTS - Request To Send (pin #7)- always at low .– DTR - Data Terminal Ready (pin #4)- always at low.

UART-Core I/O Schema

RS-232 I/F

UART-CoreControl I/F

Client I/F Data-path

Client I/FUART-statusPackets info.

UART Structure

The UART is divided into two main

sub-blocks:– Miniuart Unit : controls sending and receiving

processes.– Clock-control Units : responsible for creating the

clocks for the miniuart block, according to the host’s requested Baud-Rate.

UART Structure

Clock Control Unit

MiniUart Unit

MiniUart Structure

Consists of 6 main blocks:– 2 eb1– RCVR FIFO– RX Unit – TX Unit– XMIT FIFO – RSBusCtrl

MiniUart Structure: ”2eb1” block

Purposes:– Manages the user’s requests:

For sending data. For reading the new received data. For information about the UART’s status in polled mode.

– Preparing the data for reading by the user (checking if there are any errors ,take out the data itself from the frame ) and preparing the data for sending by the transmit unit.

– Operates the transmit/receive units and the FIFOs accordingly to the operation mode.

MiniUart Structure: The Receive FIFO (RCVR)

Consists of 3 blocks:– RCVR Controller.– RCVR Operator.– DUAL Port 16x10Bits RAM.

The Receive FIFO (RCVR): RCVR Controller block.

Purposes: – Calculates the write address and the read address,– Informs about the num of occupied slots, – Full and empty

indications

– Overflow and

underflow indications of the FIFO.

The receive FIFO (RCVR): RCVR Operator block.

Purposes: – manages the RCVR controller and the DUAL port

RAM according to the state of the receive unit and user’s requests.

MiniUart Unit:RX Block

Purpose: responsible for the receiving process:– Samples the RS-232 data line, respectively to the

serial transfer characteristics, and collects the incoming data.

– Forward the received data to the appropriate blocks, according to the operation mode.

MiniUart Unit:TX Block

Purpose: responsible for the transmitting process :– Converts and Sends the data vector to the RS-232

data line ,respectively to the serial transfer characteristics.

MiniUart Structure:the Transmitting FIFO (XMIT)

Consists of 3 blocks:– XMIT Controller.– XMIT Operator.– DUAL Port RAM.

The Transmitting FIFO (XMIT):XMIT Cotroller

Purpose :– Calculates the write address and the read

address,– Informs about the num of occupied slots, – Full and empty indications– Overflow and underflow indications of the FIFO.

The Transmitting FIFO (XMIT):XMIT Operator

Purpose : – Manages the XMIT Controller and the Dual Port

RAM , according the state of the transmitting unit and user’s requests.

MiniUart Unit:RSbusCtrl block

This block has 4 different mode of functioning, match for every operation mode of the UART: – polled/interrupt. – with FIFO support/without FIFO support.

This block is responsible for sending interrupts, based on the UART’s status and the user’s preferences.

MiniUart Unit:RSbusCtrl block

This block also informs about parity error, frame error ,overrun error and emptiness of the XMIT and RCVR FIFOs.

The outputs of this block combine the status vector, which active in polled mode.

UART - Core : Verification

An “error generator” block was build. Purpose:

– Inverse bits in the new received data, enable checking the UART’s behavior to parity and frame errors.


Sending files to the UART, using HyperTerminal and got back the correct frames that were received by the UART, number of frame errors and number of parity errors, that were generated by the “error generation”.

This was tested in all the 4 operation modes of the UART (with FIFO support/without FIFO support , interrupt /polled mode).

This was tested in all the baud rates from 2400 to 115200.


Verified/Tested corner-cases :– Correct roll-over of both of the FIFOs.– Using different RCVR Trigger of the RCVR FIFO.– Changing serial transfer characteristics during

running.– Correct overrun error in different operations

modes.


Verified/Tested corner-cases : – UART’s support of various serial transfer

characteristics :– 5,6,7 and 8-bit characters. – Even, odd or none parity.– 1,2 stop bit.

Further improvements

16850 UART- which includes a 128 bytes FIFO.

DUART- (“Dual UART”) :combines two UARTs into

a single chip . USART-(A Universal Synchronous Asynchronous

Receiver /Transmitter) : a UART that can also communicate synchronously.

Documents

By: Marganit Fina Supervisor: Rivkin Ina Winter 2007/8 Duration: Semester