SERIAL Port (RS-232)

SERIAL Port (RS-232)
By default - a START-STOP ports does not have clocking-pins (pin-15 Transmit / pin-17 Receive - Clock).


The ASYNC-Serial Interface (RS-232) is designed to work at operation speeds:

from 50-bps up to max. 19200-bps on some older machines (8250 ACIA-type)
from 50-bps up to max. 115200-bps on all other machines



Be sure (directly connected) machine setup, is defined for same SPEED (baud-rate), WORD-length
and PARITY (default use: 8-N-1 = 8-databit NO-parity 1-Stopbit)
if connected together with a Null-modem  (PC-to-PC) cable.

See > Modem Setup Strings for AT (Hayes) AT-commands for various MODEM-types.
See > Some about MODEMs

The CABLE-length/speed, depends on various facts as:


Normally a well behaved cable should work, if the total length is <= 12 meters (36 feet). And all electric/environment factors are OK.

Voltage Interchange Information

Interch. Voltage Binary State Condition Interf.-Ctrl. Funct.
Positive = Binary 0 = Spacing = ON
Negative = Binary 1 = Marking = OFF


Valid EIA Voltage (signal) Levels: (SIGNAL-GROUND to PINx)

+3 up to +15 Volt DC = ON Function
-3 up to -15 Volt DC = OFF Function
-3 up to +3 Volt DC = INVALID (defective) LEVEL


25-Pin D-shell (DB-25) Connector Pin-layout (Async- w/o clock)

PIN Signal Name   I/O PIN Signal Name   I/O
2 Transmitted Data TD O 7 Signal Ground SG  
3 Received Data RD I 8 Carrier Detect DCD I
4 Request to Send RTS O 20 Data Terminal Ready DTR O
5 Clear To Send CTS I 22 Ring Indicator RI I
6 Data Set Ready DSR I        


9-Pin D-shell (DB-9) Connector Pin-layout (Async- w/o clock)

PIN Signal Name   I/O PIN Signal Name   I/O
1 Data Carrier Detect DCD I 6 Data Set Ready DSR I
2 Receive Data RD I 7 Request To Send RTS O
3 Transmit Data TD O 8 Clear To Send CTS I
4 Data Terminal Ready DTR O 9 Ring Indicator RI I
5 Signal Ground SG          


Examples:


Serial 25-Pin IBM-PS/2 to PRINTER Cable  (for Printer XON-XOFF Protocol)
(Serial Printer Cable IBM FRU-P/N 8509386)

   COMPUTER                                PRINTER
 PIN    SGNL                             SGNL    PIN
  2     XMIT->------------+   +--------<-XMIT     2
                      +---+---+
  3     RCV -<--------+   +------------>- RCV     3
  4     RTS ->-----------+   +--------<- RTS     4
               |          |   |
  5     CTS -<-+------+   +---+-------->- CTS     5
               |  +---+-------+
  6     DSR -<-+--+   |   +------------>- DSR     6
               |      |   |
  7     GND ---+------+---+-------------- GND     7
               |      |   |
  8     DCD -<-+      +---+---+           DCD     8
                          |   |
 20     DTR ->------------+   +--------<- DTR     20


Serial 25-Pin NULL MODEM Cable 

  COMPUTER-A                              COMPUTER-B
 PIN    SGNL                             SGNL    PIN
  2     XMIT->------------+   +--------<-XMIT     2
                      +---+---+
  3     RCV -<--------+   +------------>- RCV     3
  4     RTS ->------------+   +--------<- RTS     4
                      +---+---+
  5     CTS -<--------+   +------------>- CTS     5
  6     DSR -<-------+       +------->- DSR     6
               |      |       |      |
  7     GND ---+------+-------+------+--- GND     7
               |      |       |      |
  8     DCD -<-+      +-------+--+   +->- DCD     8
                              |  |
 20     DTR ->----------------+  +-----<- DTR     20


Serial 25-Pin LAPLINK Cable  (c) Traveling Software, Inc.

   COMPUTER                                COMPUTER
 PIN    SGNL                             SGNL    PIN
  2     XMIT->------------+   +--------<-XMIT     2
                      +---+---+
  3     RCV -<--------+   +------------>- RCV     3
  4     RTS ->------------+   +--------<- RTS     4
                      +---+---+
  5     CTS -<--------+   +------------>- CTS     5
  6     DSR -<--------+   +------------>- DSR     6
                      |   |
  7     GND ----------+---+-------------- GND     7
                      +---+---+
 20     DTR ->------------+   +--------<- DTR     20


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