UARTS Interface
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Transcript of UARTS Interface
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OSI Physical Layer
Components
Digital and Data Communications
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Data Communication Link
DTE DCE DCE DTE
RS -232C RS -232C
Transmission Medium
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UART Uses
PC serial port is a UART! Serializes data to be sent over serial cable
De-serializes received data
Serial
Cable
Serial
Cable
Device
SerialPort SerialPort
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UART Uses
Communication between distant computers Serializes data to be sent to modem
De-serializes data received from modem
Serial
Cable
Serial
CablePhone
Line
Phone
Line
Modem
Modem
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Options Found in UARTs
Character Type Option for an 8-bit bus
No. of Stop bits required
Use of parity type
Use of diff. data rates
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ACIA
AsynchronousCommunications
Interface Adapter
by Motorola
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UNITS of COMMUNICATION LINK
UART
Transmitter side
needs 8 data bus lines for a 8-bit parallel
data to be converted into a serial data
stream.
Idle line one/marking state
Some are onboard
Example ACIA by Motorola
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UART Transmission Example
Send the ASCII letter W (1010111)
1
Line idling Start bit Parity bit(odd parity) Stop bit
Line idling again
Mark
Space
7 data bits Least significant bit first
1 1 0 1 0 1 0
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MC6850Pin Assignment
CPU Pin
Data Bus (D0-D7)
Control Bus (R/W, E, CS)
Address (RS, CS)
Other: IRQ
EIA-232 Pin
Data (Rx, Tx)
Control (RTX, CTS, DCD)
Baud Clock (Rx CLK, Tx CLK)
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ACIA Register Contents
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ACIA Control Register (8-bit)
7 6 5 4 3 2 1 0
RX
IR
__
RTS
TX
IR
WORD
SIZE
STOP
&
PARITY
COUNTER
DIVIDE
AC A C l i ( bi )
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ACIA Control Register (8-bit)
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UART Receiver
Use of Divide ratio
In half of the bit period where a start
bit can be verified
Use of shift register
Clock Skew
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UARTStatus Register
7 6 5 4 3 2 1 0
__
IRQ
PE OVRN FE __
CTS
__
DCD
TDRE RDRF
Ch ki UART P f
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Checking UART Performance
Use of Status Register Use of TDRE
From buffer register to the shift-register
Use of RDRF
From shift-register to the buffer register
Use of OVRN
failure to read the data from the buffer register
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Checking UART Performance
Use of Parity Error Use of Framing Error
Use of IRQ
2 conditions when IR functions at the
Control register
TDRE or RDRF is high
a received error has occurred
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RS-232C Specifications
Most common by EIA
Uses a D-type 25 pin connector
uses voltage levels of +3 to +25 V (SPACE,data 0, on, green) and -3 to -25 V (MARK, data
1, off, red)
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RS-232C Specifications
Cable impedance
330 min Tx
7000 max - Rx
Line Capacitance -2500 pf
50 pf/ foot limited to 100kb/s
Ideal for short distance less than 50ft
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RS-232C
Since the link only uses about 7 wires, DB-9
connectors are frequently used now for seriallinks,
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Handshaking Lines
DTE uses a signal called RTS on pin 4, while
DCE uses a signal called CTS on pin 5.
Data is transmitted from DTE to DCE on pin 2,
and from DCE to DTE on pin 3.
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NULL Modem
1
2
3
4
5
6
7
8
20
1
2
3
45
6
7
8
20
DTE 1 DTE 2
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RS-449
Uses D-type
connectors
37-pin
9-pin
2 Mbps transfer rate Max length -200 feet
w/ loop-back feature
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RS-422 balanced electrical interface
implemented using a D-type connector with 37 pins RS-449 specifications
logic 1 (Mark) is represented by the A output beingmore negative than the B output.
logic 0 (Space) is represented by the A output being
more positive than the B output.
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RS-423
unbalanced electrical interface
implemented using a D-type connector with 37pins RS-449 specifications
low speed communications
generally operate at +/- 6 VDC and are
compatible with RS-232 devices
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RS-423 very sensitive, capable of detecting Mark/Space
states at +/- 0.4 VDC
has separate Signal Grounds for transmitters andreceivers
A binary one (Mark) is represented by a Negativevoltage level
and a binary zero (Space) is represented by a
Positive voltage level.
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ASSIGN:
USB interface standards How to interface a PC to PC using USB port?