UART

2.0 The design Architecture

The UART implements the RS-232 serial communication protocol.RS232 connector is a port used for data exchange between equipments. It was designed for data exchange between DTE (Data Terminal Equipment) or PC and DCE (Data Communication Equipment) or MODEM using serial pinouts of either the DB9 or DB25 variety. In a laymans terms DTE are devices that process digital signals they are data endpoints like laptops, printers, calculators, POS etc and most digital devices, while DCE are devices that does DAC/ADC (digital to analog or analog to digital conversion), they transmit and receive data for DTE .

2.1 An RS232 pinout 9 pin cable features nine pins:

• 1. Carrier Detect:Carrier Detect(Set by MODEM when answer is received by remote MODEM ).


• 2. RXD: Receive Data (Data is received though this pin)


• 3. TXD: Transmit Data (Data is transmitted through this pin)


• 4. DTR: Data Terminal Ready(Set by PC to prepare MODEM to be connected to telephone circuit)


• 5. DSR: Data Set Ready(Set by MODEM to tell PC it is ready to receive and send data)


• 6. RTS: Request To Send(Set by PC to tell MODEM that MODEM can begin sending data)


• 7. CTS: Clear To send(Set by MODEM to tell PC that it is ready to receive data)


• 8. RI: Set by MODEM to tell PC a ringing condition has been detected.


• 9. GND: Ground (Used as reference for all pin voltage pulses).

2.2 The UART design

We would design a 16-bit UART transceiver consisting of the baud generator, receiver and transmitter. I will give both the circuit diagram from Logism, the vhdl code and the verilog code. The HDL codes are made very simple so that the concept will easily be understood. We will build the UART from ground up and join the subcircuits level by level using VHDL and Verilog function.The only subcircuit not included is the parity generator which is associated with the transmitter, we will discuss that in later chapter. The baud generator will generate from the system clock, the common baud agreed upon between the transmitter and receiver. as will be seen in our next chapter.
Both receiver and transmitter have the FSM(Finite State Machine) subcircuits this is used to move the trnasmission and reception of data stage by stage from when the transmitter initiates to send data to when the data is completely sent and received by the receiver. The state action subcircuits determines what happens at each stage.

UART Transceiver subcircuit Tree.