Jim Robertson wrote: > As best I can tell the USB pics only support low speed mode and > while 1.5Mb/S seems fast the actual "useful" transfer speed is > something like 8 bytes per 10mS. Ok for some things but not a high > speed PIC programmer say. > > Now watch someone like Andy Warren shoot me down in flames. ;-) Jim: No flames; you're correct on all counts. The USB PICs only support the lowest-speed (1.5 Mbps), lowest- functionality mode of USB, and low-speed devices max out at one 8- byte packet per 10-ms polling interval, or 800 bytes/second. You can get a little extra speed by doing antisocial things like sending data over a "control" endpoint, but even that won't let you do much better than 1000 bytes per second. Full-speed (12 Mbps) devices can transfer bulk data over one thousand times faster: A full-speed chip like Cypress's EZ-USB FX can transfer 19 64-byte packets per 1-millisecond frame. 19 * 64 * 1000 = 1,216,000 bytes per second. Most PCs are only fast enough to schedule 17 packets/frame... But even at that speed, full-speed devices can do one million bytes per second. High-speed devices -- like, say, Cypress's EZ-USB FX2 -- are currently moving five 512-byte packets per 1/8-millisecond microframe. 5 * 512 * 8000 = 20,480,000 bytes per second. With real PC-side drivers (Microsoft's current USB 2.0 drivers are still in beta), transfer rates should get close to 40,000,000 bytes/second. -Andy === Andrew Warren --- aiw@cypress.com === IPD Systems Engineering, CYSD === Cypress Semiconductor Corporation === === Opinions expressed above do not === necessarily represent those of === Cypress Semiconductor Corporation -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.