So another thought is that since there is a Tx enable in the hm2 module it's obviously there for a reason. rs485 is always emphasized but rs485 is mentioned in alot of cases as well. In the case of an 8i20 it includes jumpers to enable bus termination resistors. So I'm wondering if using the Tx enable on the driver would technically make it rs485 so you could run multiple devices like 8i20s or smbl drives on one channel. There could be other considerations like latency issues or something, just curious if that would work.
On Sunday, July 7, 2019 at 8:36:39 PM UTC-4, justin White wrote: > > > > On Sunday, July 7, 2019 at 2:16:22 PM UTC-4, Charles Steinkuehler wrote: >> There's good info in the data sheet for that part: >> http://www.ti.com/lit/gpn/thvd1451 >> ...which is an RS-485 transceiver (RS-485 is the same electrically as >> RS-422, but the driver can be switched off). >> RS-485 is a "multi-drop" protocol, and supports multiple transceivers. >> Typically, the end nodes will have termination resistors populated >> and the devices in the middle on the cable will have the termination >> disabled. See figure 32 (page 22) in the data sheet. >> PCW said it's straight RS-422, not RS-485. That means you only have >> two devices making each device an end point, so add termination to >> both ends. > > > That's kind of unfortunate because you'd need a separate channel for each > device. Now my head is spinning again because my encoders and stepgens are > differential recievers/drivers so I could technically pretty much just > repurpose one of each and get a couple of channels out of one set of > connectors. I didn't put any impedance control or TVS on them but now I'm > thinking if I make some accommodations I can just sacrifice encoders and > stepgens for serial channels. > > > The ESD protection is application dependent, but you might also want >> a small value series resistor between the THVD1451 and the cable (see >> Figure 38, page 27 along with the recommend parts list) and see the >> layout recommendations on page 29. > > > >> ...but don't sweat the details too much. For a short range (a few >> meters) point-to-point connection, the ESD and even the termination >> resistors are not super important. I'd still add them (it's cheap >> insurance!), but I don't expect you're designing for 1.5 km long >> cables that need to withstand nearby lightning strikes. :) >> That said, spindle motors can throw off enough ESD to cause problems >> even with differential signals, which is why you want _something_. > > > I just whipped the drawing up this morning, I was originally going to use > a different chip and had a different drawing. Good to know it's on the > right track though. > > tvs and esd are somewhat of a concern since while I didn't really intend > it, I can pretty much replace the x86 PC and 7i76e on my mill with this. In > that case I use an 8i20 for my spindle with a power supply that consists of > some big caps, a couple of SSRs and a bridge rectifier. There's 240v AC > going into that box 320v DC coming out. While I shielded all cables, a > little protection on the data lines is probably a good idea. Not sure of > the performance of the DE10 Nano itself just yet since I just load up an > Axis config and fire up halshow for the time being. Unless I converted my > mill I probably wouldn't have an actual machine to run on this any time > soon. > > Every time I think I'm damn near done with it I come up with something > else to complicate things lol. > -- website: http://www.machinekit.io blog: http://blog.machinekit.io github: https://github.com/machinekit --- You received this message because you are subscribed to the Google Groups "Machinekit" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. Visit this group at https://groups.google.com/group/machinekit. To view this discussion on the web visit https://groups.google.com/d/msgid/machinekit/6df1fef2-f29b-4019-b58e-0b6492a07be5%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
