On 23 October 2010 13:58, Andy Ibbotson <andyi_w...@btinternet.com> wrote: > > Thanks Andy. I thought that EMC2 required EPP mode on the parallel port
AFAIK only for devices that use it for communications, not for applications which simply twiddle the pins on and off as individual signals. I might be mistaken. > think people are using the board to drive software stepgen. Yes, it has a nice low latency which suits that. > Going back to the PCI based cards, does the extra speed of the interface > mean that the servo thread can be run faster giving increased update rates > of velocity? Possibly. I have read somewhere that a sane (200uS) servo-thread _execution_ period is only enough time to shift 50 bytes through a parallel port. That is potentially limiting, but has not been a problem I have noticed with my 4-axis machine. The software stepgens running in the base thread and twiddling pins individually are effectively shifting one word per thread cycle. > I'm trying to assess the benefits of moving from software > stepgen to hardware stepgens. The main "win" is possibly fast encoder counting for spindle encoders. The advantage from a stepgen point of view is reduced granularity of step timings at higher rates. with a 20uS base thread you hit the point where your step time gets quantised into 80uS, 60uS, 40uS or 20us (with x8 microstepping and 200ppr that's 470rpm, 625rpm, 940rpm and 1880rpm) and you are effectively asking your motor to instantaneously accelerate between the speeds which is asking a lot of a motor which is probably already running out of torque a those speeds. Another huge advantage is that suddenly you have GPIO pins in abundance. -- atp ------------------------------------------------------------------------------ Nokia and AT&T present the 2010 Calling All Innovators-North America contest Create new apps & games for the Nokia N8 for consumers in U.S. and Canada $10 million total in prizes - $4M cash, 500 devices, nearly $6M in marketing Develop with Nokia Qt SDK, Web Runtime, or Java and Publish to Ovi Store http://p.sf.net/sfu/nokia-dev2dev _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
