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RS-232 BASICS

As related to PacketRadio

Serial data transmission.

Serial data transmission is the most common method of sending data from one DTE to another. During transmission, the data must pass through a serial interface to exit a computer as serial data. PacketRadio terminal node controllers (TNCees) employ two types of common interface connectors for serial data transfer. These connectors are:

1. DB25
2. DE9 but more often called; the DB9

The RS-232 interface is ideal for the data-transmission up to about 20,000 bits per second, to about fifty (50) feet, or around fifteen (15) meters. RS-232 employs unbalanced signaling and is usually used with DB25 connectors to interconnect data terminal equipment [DTE] (computers, controllers, etc), to data communications equipment [DCE] (terminal node controllers/TNCees modems, etc).


The illustration above, provides a view of the standard RS232 signals as applied to the DB25 connector. Notice that signals/pins 2, 3, 4, 5, and 7, are the most commonly used signals for PC (DTE) to PacketRadio TNCees (DCE).

To simplify the RS232C signal definitions, I am providing the following RS232C Signal Function Table with Pin Designations relating to both the DE/DB9 and DB25 connectors.
EIA RS232-C Standard

Connector Pin Assignments

DB-25
pin #		 DB-9
pin #		 Name Description
1 PG Protective Ground
2 3 TD Transmitted Data
3 2 RD Received Data
4 7 RTS Request To Send
5 8 CTS Clear To Send
6 6 DSR Data Set Ready
7 5 SG Signal Ground
8 1 DCD Data Carrier Detect
9 -- Reserved for testing
10 -- Reserved for testing
11 -- Unassigned
12 SDCD Secondary Data Carrier Detect
13 SCTSSecondary Clear To Send
14 STDSecondary Transmitted Data
15 TCTransmission (signal) Timing
16 SRDSecondary Received Data
17 RCReceiver (signal) Timing
18 --Unassigned
19 SRTSSecondary Request To Send
20 4 DTRData Terminal Ready
21 SQSignal Quality Detect
22 9 RIRing Indicator
23 --Data Rate Selector
24 --Transmit (signal) Timing
25 --Unassigned

NEVER, as in ''DO NOT'' connect protective ground (DB25, pin 1) to signal ground (DB25, pin 7)

db25r232.gif - 9653 Bytes
This DB25 (DTE) to DB25 (DCE) interface cable is most used between the PC and the AEA/Timewave, Kantronics, and MFJ terminal node controllers.


Where the PC utilizes a DB9 comport, the numbering scheme at the PC end of the cable varies from the wiring scheme of the DB25.


The late model PacComm and DRSI TNCees employ the DE9 (DB9) comports. The illustration above provides a view of the wiring scheme for a DB25 DTE to DB9 DCE interface.

Serial data exits through an RS-232 communications port (comport) via the Transmit Data (TxD) lead and arrives at the destination device’s RS-232 comport through its Receive Data (RxD) lead.

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If these RS232C BASICS were help to you, please let us know:

Buck "[email protected]"

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