tag:blogger.com,1999:blog-497171217098538004.post5050630717476258519..comments2023-09-15T02:40:43.650-07:00Comments on Boat Projects: Beginners guide to Nmea 2000, Nmea 0183, and bridgingPaulhttp://www.blogger.com/profile/09320074079673445090noreply@blogger.comBlogger2125tag:blogger.com,1999:blog-497171217098538004.post-85956989653891484242013-10-06T06:21:16.974-07:002013-10-06T06:21:16.974-07:00The NMEA 0183 was fine when originally implemented...The NMEA 0183 was fine when originally implemented. It used a simple pull up/pull down bus driver transistor combination on a tri-state floating bus with 1.2k node impedance. What you refer to as talkers could share the same bus. You are right, they shared a common ground but back in those days isolation was very difficult so the original idea was to isolate the PSU so as not create what we used to call false negatives. However this all got a bit confused somewhere along the way! It is not quite serial as in the strict timing sense of 8250/16550 USARTs etc because it was based around the Z80 with a three times over-sample, that meant I had to guarantee a three stop bit gap between sentences. Thats why I had to use 4800 not 9600 (as per the original design) because we couldn't in the software sample the start using a Z80 at 9600 and maintain the sample points at the correct intervals, it wasn't about distance it was about interrupt code. It can drive very long distances, 30m is not uncommon, the issue was always the drive up power whilst remaining decoupled, remember in those days, MosFET etc were ridiculously expensive devices with huge capacitive issues! You may be interested to know that originally it was developed as a marine engine management monitoring system but was 5 years ahead of technology and was adopted by NMEA as a marine instrumentation system.<br />Regards Paul Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-497171217098538004.post-61222174105927282262013-09-08T22:49:44.407-07:002013-09-08T22:49:44.407-07:00I'm a garmin tech support rep. This is very he...I'm a garmin tech support rep. This is very helpful. Keep it up! Anonymousnoreply@blogger.com