On Thu, Jan 20, 2011 at 11:05:39AM -0800, Kirk Wallace wrote: > > The main theme is to use the data rich but speed poor parallel port to > feed a speed rich AVR using EPP, with very low latency, in an open and > DIY friendly way.
Now that sounds like fun. > The ATxmega runs on 3.6V max, so my current task is to design a parallel > port interface that can use 3 to 5V in, and feed ~3V to the xmega. After > the data link is worked out, the xmega can be used to produce a wide > range of signals (step/dir, PWM, 3-phase) and capture input (encoders, > ADC). Kirk, are you thinking of using something like an A4 xmega, in a 44 pin TQFP, for ease of soldering, or going for more I/O? (Eagle has 44 and 100 pin TQFP macros.) Ah, I see the xmega100 breakout board. It adds $19 to the chip price. We can have a prototype PCB done for that, if it fits within 6.3 x 4 inches. Still, I've only hand soldered TQFP44, using a hollow-tipped iron. That was so easy. TQFP100 is said to be manageable as well. One option is to lay out the PCB for the breakout board _and_ an xmega100 within that. Then it can be built either way. I see that "Absolute Maximum ratings" won't allow feeding in 5v signals, but TTL levels would just about be OK if Vcc is near 3.6v. Some resistive dividing could add a safety margin, but clamping to Vcc (e.g. 3.3v) via schottky diodes, with resistors on the inputs, would provide more consistent input voltages with a greater variety of PP implementations. For xmega to 5v conversion, a common emitter transistor with (say) 4k7 on the base, and 1k on the collector, would suffice. If there are no more than 5 xmega -> PP signals, then a small transistor array like the LM3046 would save fiddling with individual transistors. (An SMD LM3046 is convenient, individual SOT23 transistors are a pain, I find.) > If there is enough interest, it might be worth while to have a batch of > PC boards made and/or maintain a parts list or kits. It costs so little to have even one made, that I'd do schematic capture, have several of us check the design, do the layout, send the eagle file off, and have a cheap first prototype back inside a week. If a track or two need to be cut, and a wire run, then that's normal. Since an ATxmega128A1 is about $11, the whole interface PCB plus CPU can be had for the same money as the xmega100 breakout board. (If out eyesight is up to it. :-) Just some initial thoughts. Erik ------------------------------------------------------------------------------ Special Offer-- Download ArcSight Logger for FREE (a $49 USD value)! Finally, a world-class log management solution at an even better price-free! Download using promo code Free_Logger_4_Dev2Dev. Offer expires February 28th, so secure your free ArcSight Logger TODAY! http://p.sf.net/sfu/arcsight-sfd2d _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
