Motorola USB08 Betriebsanleitung PDF herunterladen (Seite 89)

APPENDIX F - RS232 COMMUNICATIONS

Introduction

The RS232 standard, now more correctly the EIA232 standard, first appeared in the 1960's. It was

originally written to standardize the interconnection of terminals and modems, in the days when one

mainframe computer hosted many remote terminals. In the standard, a terminal is referred to as a DTE

(Data Terminal/Terminating Equipment), and the modem as a DCE (Data Communication

Equipment). This primer is a brief introduction to the standard, and to the signaling protocol usually

employed, from the perspective of a Xplor8 user who just wants to 'get it all to work'

Physical Connectors

The DTE is traditionally fitted with a male 'D' connector, and the modem (DCE) with a female one.

When the IBM personal computer first appeared it had serial or 'COM' ports which were implemented

as RS232 standard 25-pin male 'D' connectors on the back panel. When the AT version of the PC

appeared, IBM began to adopt a nine pin version of the 'D' connector, and this is now universal on

personal computers that still have hardware serial ports.

One pin is reserved as the common signal return or ground pin (5). Two pins are used for full duplex

data transfer (2,3). The remaining six pins all carry handshaking information to control the flow of data

on TxD and RxD.

The pinout, looking on the outside of the male DB9 connector as found on the back of a PC, is as

follows:

1 2 ... 84 85 86 87 88 89 90 91 92 93 94 ... 99 100

Keine Kommentare

Motorola USB08 Betriebsanleitung Seite 89