Introduction to Microcontrollers Lab Manual - Microchip

3.1 OBJECTIVE
3.2 PRE-LAB
Lab 3. UART
This lab covers the following concepts:
• PIC24F UART Hardware Module
• PIC24F Peripheral Pin Select Hardware Module
• ASCII Character Encoding
3.2.1 Reference Material
• PIC24FJ256GB110 Data Sheet (DS39897)
• 16-Bit MCU and DSC Programmer’s Reference Manual (DS70157)
• MPLAB IDE User’s Guide (DS51519)
• PIC24F Reference Manual – Section 8. Interrupts (DS39707)
• PIC24F Reference Manual – Section 12. Peripheral Pin Select (DS39711)
• PIC24F Reference Manual – Section 21. UART (DS39708)
3.2.2 UART (Universal Asynchronous Receiver/Transmitter)
LABS
A UART is a piece of hardware that uses a shift register to convert data between serial
and parallel forms. As the name implies, each UART actually contains two pieces of
hardware and therefore two shift registers, a Receiver (Rx) and a Transmitter (Tx).
Simplified, a UART transmitter takes bytes (8 bits) of data and transmits them as individual
bits in sequential fashion. Then another UART receiver at the other end takes
those sequential bits and re-assembles them back into bytes.
The simple reason for this is that serial transmission across a single wire is much more
cost effective then parallel transmission across multiple wires.
The communication is actually a little more complicated then described above. The
UART is an “asynchronous” receiver/transmitter. Therefore, some synchronization
between transmitter and receiver is required. To accomplish this, both the transmitter
and receiver must run at the same baud rate with a START and one or two STOP bits
inserted into the serial bit stream. Parity bits can also be inserted into the bit stream for
error detection. Figure 3-1 illustrates all possible bits in a serial bit stream.
FIGURE 3-1: LAB 3 SERIAL TRANSMISSION OF BYTE
A standard embedded UART configuration is 8 bits of data with no parity bit and one
stop bit. This is also referred to as 8N1 and is illustrated in Figure 3-2.
2011 Microchip Technology Inc. DS51963A-page 25