What is System Programming?

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• Lecture 13

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C\gtdebug-o 378 0A-i 379D0-o 378 19-i
37948
Sending byte 9A
C\gtdebug-i 379D7-o 378 0A-i 3794F-o 378 19
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0A00001010 , Data line 40 (sent)D711010111
, BUSY1 (recieved)11010111 gtgt 3 00011010
00011010 00001111 00001010 0A , Data line
4 0 (send for verification)D0 11010000 ,
BUSY1 (received verified)
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0900001001 , Data line 4 0Set Data line 4 to
100001001 00010000 00011001 19 ,(Sent to
378H) (Sent)4FH01001111 , BUSY0
(Received)01001111 ltlt 1 1001111
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Joining both nibblesLow Nibble00011010
00001111 00001010Hi Nibble10011111
11110000 10010000Whole byte00001010
10010000 10011010 9A
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int i 0 char Buf1024 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 gtgt
4 ch ch 0x10 outport (lpt,
ch) i while((inport((lpt)
1) 0x80) 80)
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int i while (1) if ((inport(lpt 1) 0x80)
0x80) x inport ((lpt) 1) x x gtgt
3 x x 0x0F outport((lpt), x)
while((inport(lpt 1) 0x80)
0x80) else y inport ((lpt) 1) y
y ltlt 1 temp y y y x
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temp temp gtgt 4 \\ Move to Low Nibble
temp temp 0x10\\ Set D4 bit i
outport (lpt, temp)\\ Send for
verification Buf i y
while((inport((lpt) 1) 0x80) 0)
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Serial Communication

• Advantages
• Disadvantages

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Types Of Serial Communication

• Synchronous
• Asynchronous

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Synchronous Communication

• Timing signal is used to identify start and end
  of a bit.

0 1 1 0 1 0 1 1
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Synchronous Communication

• 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).

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Asynchronous Communication

• Does not use make use of timing signal.
• Each byte (word) needs to encapsulated in start
  and end bit.

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Serial Communication using a UART
Parity bit
Start bit of next byte
0 1 2 3 4 5 6 7 8
1 0
5 8 bit
1, 1.5, 2 Stop bit
Start bit

• 1.5 Stop bit

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Sampling Rate
Bit rate 9600 A bit is sampled
after 1/9600 -- 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
start bit (low) at the start of Byte is used to
identify the start of a Byte.
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Sampling Rate

• -- Bit rate and other settings should be the same
  at both ends i.e.
• Data bits per Byte. (5 8 )
• Parity check
• Parity Even/Odd
• No. of stop bits.

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Sampling Rate
1/1300 sec
Data bits
Stop bit
Start bit
Odd parity
A 41H 0100 0001 B Parity Odd Data
8 Stop bit 1 Data rate 300 bits/sec

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RS 232C Standard

• Standard for physical dimensions of the
  connectors.

RS 232C Cable
PC (DTE)
(DCE)
Modem
Connected via serial port
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RS 232C Connectors and SignalsDB25 (25 pin
connector)
13
25
12
24
11
23
10
RI
22
9
21
CD
8
DTR
20
GND
7
19
6
DSR
18
5
CTS
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4
RTS
18
3
RD
19
2
T X D
20
1
25 pin connector on PC
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RI
CD
DTE
DCE
DTR
PC
MODEM
DSR
RTS
CTS
RxD
TxD
DTR (SHOULD REMAIN HIGH THROUGH OUT THE SESSION )
CTS (CAN BE USED FOR FLOW CONTROL )