Part 2

Interface Concepts 63 1STARTBITPARITY BITfOPTIONALl\ JCHARACTERILENGTH=7 OR 8 BITS1\FIRSTSTOPBITSECONDSTOP BIT[USED ONLY FOR llObpslDATA DIRECTlONFigure A-3. Asynchronous Character StructureWhen data is not being transmitted, the line is idle (low or mark). The transmittingdevice drives the line high (space) for one bit time when it has a character to send,hence the name start bit. The actual character is then transmitted, followed by aparity bit (optional when the 3497A is configured for 8-bit ASCII). The stop bit(s)is then sent which involves the transmitting device holding the line low (mark) forone or two bit times. The actual character transmission is shown in Figure A-4,which, in this instance, is the 7-bit ASCII representation of the letter "E". A moredetailed explanation for each part of the character transmission follows Figure A-4.STARTBITSPACE (HIGH1 I+ [LSBIIDLE STATE-MARK ILOWl - -1 0 1 0 0 0 1I-PAR1 TYBIT-STOPBIT (SI----DATA DIRECTION-Figure A-4. Asynchronous Character TransmissionIdle StateThe line is held at this low voltage level (mark) when no character is beingtransmitted.Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com