| ??? 07/06/06 17:04 Read: times |
#119752 - slew rate controlled - low speed ?? Responding to: ???'s previous message |
Sometimes simply exchanging the RS485 driver by a slew rate controlled one is enough to pass the CE-tests... Looks like the data rate is not the same for normal devices and slew rate controlled devices! The following text is from the respective data sheet: Sipex part SP485: The transmitters of the SP481 and SP485 will operate up to at least 5Mbps. The SP483 has internally slew rate limited driver outputs to minimize EMI. The maximum data rate for the SP483 driver is 250kbps. Analog Devices part ADM485: The ADM485 features extremely fast switching speeds. Minimal driver propagation delays permit transmission at data rates up to 5 Mbps while low skew minimizes EMI interference. Linear Tech LT1785: Data rates to 250kbaud on networks of up to 128 nodes are supported. Controlled slew rates on the driver outputs control EMI emissions and improve data transmission integrity on improperly terminated lines. The Analog Devices data sheet is not clear about the data rate. I have chosen to cut from the data sheets of the above two parts (ADM and SIPEX) is simply because those were the ones available here, and I have purchased them for my RS485 products. By the way, what is the maximum, practical, reliable data rate used for a cable of 1000 meters in length? John. |
