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Introduction to Data Communications
17b. Electrical Characteristics of the RS-232D (cont'd)
The receiving side recognizes a Space (digital 0 or Low) as any voltage between +3 and +25V and a Mark (digital 1 or High) as any voltage between -3 and -25V. The standard allows for a voltage loss through the cable and noise immunity by reducing the receive requirements to +/-3 Volts!
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Pin
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Name
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Description
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EIA Circuit
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1
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GND
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Chassis ground
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AA
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2
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TXD
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Transmit Data (TXD)
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BA
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3
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RXD
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Receive Data (RXD)
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BB
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4
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RTS
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Ready to Send
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CA
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5
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CTS
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Clear to Send
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CB
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6
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DSR
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Data Set Ready (DCE Ready)
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CC
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7
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SGND
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Signal ground
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AB
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8
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DCD
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Carrier Detect (CD or RLSD)
(RLSD - Received Line Signal Detector)
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CF
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9
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n/u
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|
|
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10
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n/u
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|
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11
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n/u
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|
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12
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DCD2
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Secondary Carrier Detect (SRLSD)
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SCF
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13
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CTS2
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Secondary Clear to Send
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SCB
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14
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TXD2
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Secondary Transmit Data
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SBA
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15
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TxSigC
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Transmitter Signal Element Timing - DCE
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DB
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16
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RXD2
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Secondary Receive Data
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SBB
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17
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RxSig
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Receive Signal Element Timing - DCE
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DD
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18
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LL
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Local Loopback
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19
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RTS2
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Secondary Ready to Send
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SCA
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20
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DTR
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Data Terminal Ready (DTE Ready)
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CD
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21
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SQ/RL
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Signal Quality/Remote Loopback
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CG
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22
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RI
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Ring Indicator
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CE
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23
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DSRS
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Data Signal Rate Selector
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CH/CI
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24
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TxSigT
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Transmitter Signal Element Timing - DTE
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DA
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25
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TM
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Test Mode
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The signals in Bold/Italic are required for a basic asynchronous modem connection.
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