Download Serial Communication: Implementation and Types and more Study notes System Programming in PDF only on Docsity!
Lecture # 13
Program implementing the described protocol
int i= 0; char Buf[1024]; while (1) { ch = Buf [i]; if ((inport((lpt) + 1)& 0x80) == 0) { ch = Buf [i]; ch = ch & 0xEF; while((inport((lpt) + 1) &0x80) == 0); } else { ch = Buf [i]; ch = ch >> 4; ch = ch | 0x10; outport (lpt, ch); i++; while((inport((lpt) + 1) &0x80) == 80); } }**
This is the sender program. This program if find the BUSY bit clear sends the low nibble
but turns the D4 bit to 0 before sending. Similarly it right shifts the byte 4 times sets the
D4 bit and then sends the high nibble and waits for acknowledgment until the BUSY is
cleared.
int i;
while (1)
{ if ((inport(*lpt + 1)& 0x80) == 0x80)
{ x = inport ((*lpt) + 1);
x = x >> 3;
x = x & 0x0F;
outport((*lpt), x);
while((inport(*lpt + 1) &0x80) == 0x80);
else
{ y = inport ((*lpt) + 1);
y = y << 1;
temp = y;
y = y & 0xF0; //instruction added
y = y | x;
temp = temp >> 3; temp = temp | 0x10; i++; outport (lpt, temp); Buf [i] = y; while((inport((lpt) + 1) &0x80) == 0); } }**
This is receiver program. If the BUSY bit is clear it receives the low nibble and stores it
in x. Similarly if the BUSY bit is 0 it receives the high nibble and concatenates the botth
nibble to form a byte.
In case of synchronous communication as shown in the slide a timing signal is required to
identify the start and end of a bit.
- Sampling may be edge triggered.
- Special line may be required for
timing signal (requires another line).
- Or the timing signal may be encoded
within the original signal (requires
double the bandwidth).
Synchronous Communication
Asynchronous Communication
- Does not use make use of timing
signal.
- Each byte (word) needs to
encapsulated in start and end bit.
Asynchronous Communication
In case of asynchronous communication no timing signal is required but each byte needs
to be encapsulated to know the end and start of a byte.
UART (Universal Asynchronous Receiver Transmitter)
Serial Communication using a UART
5 – 8 bit
Start bit 1, 1.5, 2 Stop bit
Start bit of next byte
Parity bit
The UART is a device used for asynchronous communications. UART is capable o
encapsulating a byte that might be 5,6,7 or 8 bits wide in start and stop bits. Moreover it
can attach an extra parity bit with the data for error detection. The width of stop bits may
also vary.
Bit rate = 9600
A bit is sampled after = 1/
-- But start and end bits of a particular
Byte cannot be recognized.
-- So 1.5 stop bit (high) is used to
encapsulate a byte. A low start bit at
the start of Byte is used to identify the
start of a Byte.
Sampling Rate
RS – 232C Standard
- Standard for physical dimensions of the
connectors.
PC
(DTE)
Modem
RS – 232C Cable
Connected via serial port
(DCE)
RS232C is a standard for physical dimension of the connector interconnecting a
DTE(Data terminal equipment) and DCE (Data communication equipment).
RS – 232C Connectors and Signals DB25 (25 pin connector)
(^1) 25 pin connector on PC
2
9
7
8
4
5
6
10
11
12
13
3
25 24 23 22 21 20 19 18 17 16 15 14
RI CD DTR GND DSR CTS RTS RD T X D
The pin outs of the DB25 connector used with RS232C is shown in the slide above.
