UPC EETAC Bachelor's Degree in Telecommunications Systems and in Network Engineering EEL

 

USART (universal serial asynchronous receiver and transmitter)

P8

Dedicated processor (datapath + control unit)

1. Specifications

Let us design an USART. Fig. 1 shows the typical signal frame.

signal
Fig 1. Signal to transmit a byte of information.   

Note: This project follows former CSD naming conventions and styles and is not updated.

This is a reference to read about these circuits.

Example 1: Here you are an example classical chip from National Semiconductor, which was included in the firsts IBM PC in the eighties, the 8251A (or the INS8050), which is obsolete nowadays as a dual-in-line (DIL) chip component, due to the fact that its functionality is completely embedded in all microcontrollers, like in the PIC16F877A. We try to design here a simplified version of this chip. 

8251A
Fig 2. Classic USART chips.  

Example 2: Intellectual Property (IP) from Lattice Semiconductor on the reference design of a UART that can be synthesised in Lattice low-power and low-cost PLD. Note how a component like this one is professionally presented: Datasheet, VHDL and Verilog source files, testbench ("do" files), and an implementation guide to synthesise it all into a Lattice PLD using ispLEVER software (free and very similar to Altera's Quartus Prime or Xilinx Vivado). Open the datasheet and take a look at the transmitter and receivers'  state diagrams.

Lattice USART
Fig 3. Lattice USART intelectual property.  

Example 3: Intellectual Property (IP) from Intel also includes an UART that is compatible with the standard (and obsolete) chip 16550 UART from National Semiconductor (What Happened to National.com?). SC16C550B is another newer version from NXP. Companies like Eureka Technology or Digital Core Design designs specialised IP.

Thus, after studying this theory and commercial applications, let's draw our UART's block diagram.

Diagram
Fig 4. Block diagram proposed for this project.

 

2. Plan C2 based on a dedicated processor

The plan includes the problem division into several blocks, some of which were designed in previous exercises. Additionally, each cooperative group will be in charge of a different sub-module.

Block 1: Baud rate generator.

Baud rate generator
Fig 5. Baud rate generator.

 

Block 2: Transmitter datapath + Control Unit

Which resources are included in the transmitter datapath?

How does ths control unit work? Can you draw its stte diagram?

Here you are a file containing some sketches on the transmitter dedicated processor architecture. An example timing diagram (Visio).

Frame
Fig 5. Transmitter signals. 

 

 

Block 3: Receiver datapath + control Unit

Here you are a file containing some sketches on the receiver dedicated processor architecture.

receiver frame
Fig 5. Receiver signals. 

 

Block 4: Debouncing filter to generate "clean" and synhronosed digital pulses.

 

 Analyse the tutorial in P6.  

 

3. Development

There is a great deal of structural work here. Basically, a good strategy to finish the problem is the following:

 

Block 1: Baud rate generator. It works from the 50 MHz oscillator available in the DE0 board.


Chip 1: Baud_Rate_Generator

All outputs are square waveforms

(6 files)		 Chip 1:
Freq_Div_326.vhd		  
Chip 2: Freq_Div_8.vhd  
Chip3: Freq_Div_96.vhd  
Chip 4: Freq_Div_100.vhd  
Chip 2: T_flip_flop.vhd

 

Block 2: Transmitter datapath + Control Unit

Synthesise the project for an Intel chip and verify it in the laboratory. There are several options in order to perform a demonstration:

Transmiter
Fig 5. Top module pin assignment connections.  

 

Tera

ADM3202
Fig 5. ADM3202.  

 

 

Board
Fig 5. ADM3202 to adapt voltage levels to RS232 standard.

Transmitter Unit

Transmitter datapath

Transmitter control unit

Block 3: Receiver datapath + control Unit

Receiver unit

Receiver datapath

Receiver control unit

 

Block 4: Debouncing filter to generate "clean" and synhronosed digital pulses. Analyse the tutorial in P6.

Number of VHDL files involved Top block to be designed
1 Debouncing_filter.vhd

Do file to simulate pulses for the debouncing filter. Debouncing_filter_functional_ModelSim.zip

 

UART Module top design (individual VHDL source files on the above table). Below other similar projects:

UART_module_Demo_DE0.zip

UART_module_Demo_DE0_finished.zip

UART_module_SQUARED.zip

 

Number of VHDL files involved Top block to be designed Components (hierarchy level 1) Components (hierarchy level 2) Components (hierarchy level 3)
 22 

(some components are used in more than one
entity)		 UART_module.vhd Block I

Chip 1: Baud_Rate_Generator

All outputs are square waveforms

(6 files)		 Chip 1:
Freq_Div_326.vhd		  
Chip 2: Freq_Div_8.vhd  
Chip3: Freq_Div_96.vhd  
Chip 4: Freq_Div_100.vhd  
Chip 2: T_flip_flop.vhd
Block II

Chip 2: Transmitter_unit.vhd

(8 files)


 		 Chip 1: Transmitter_datapath.vhd  data_register_8bits.vhd
 shift_register_10bit.vhd
mux4.vhd
parity_generator_8bit.vhd
counter_mod8.vhd
Chip 2: Transmitter_control_unit.vhd  
Block III

Chip 3: Receiver_unit.vhd

(9 files)
 Chip 1: Receiver_datapath.vhd Chip 1: data_register_8bits.vhd
Chip 2: shift_register_10bit.vhd
Chip 3: parity_checker_9bit.vhd
Chip 4. counter_mod4.vhd
Chip 5. counter_mod8.vhd
Chip 6: counter_mod10.vhd
Chip 2: Receiver_control_unit.vhd  
Block IV

Chip 4. Debouncing_filter.vhd


(1 file)		        

 

4. Test (functional)

Once all the four blocks are finished and tested, integrate them all into the top UART (UART_module). And, once done, test it first using ModelSim. The following picture shows a demonstration where the transmitter is looped to the receiver, so that the TX_IN vector must appear at the RX_OUT once the transmission finished.

Demo1
Fig 5. Loop to simplify the test.  

 

5. Test (gate-level)

 

 

6. Prototyping

 

 

7. Report