sicklittlemonkey wrote:
On Apr 3, 4:53 am, Alex Freed <alex_n...@mirrow.com> wrote:IFAIK the EDD+ card used a regular controller plus a single (data) wire processed by dedicated logic. The same is easy to do on CB. Much easier than building a special interface for a floppy with 12V, etc.It only uses the drive's read pulse line, yes, but the floppy drive actually connects directly to the EDD+ card as shown here: http://www.apple2info.net/hardware/edd/edd.htm The goal with any similar card would hopefully be for a similarly simple installation, so that software could be captured by an average user without soldering skills. For this exact reason I tried to create a one-chip "Poor Man's EDD+" card by reprogramming the sequencer ROM. At a high enough sampling rate (2 sequencer clocks/CPU clock) this looks promising, but the Apple II doesn't have the bandwidth or memory to do much with the data. (There are other approaches too, but anyway ...)
Nick, to capture the bitstream it is only necessary to continue to shift read data into the shift register continuously, then sample it (by loading it and storing it into memory) often enough that no bits are unobserved. The Apple's speed is sufficient to do this without a problem. The problem is figuring out exactly how many shifts have occurred since the last read (since the read data could be a stream of 1's, for example). The "start bit" on each legal nibble solves this problem for normal data, but doesn't apply to register samples that are taken "mid-nibble". If it were possible to preset the shift register to $02, say, then sample at least every six shifts, the position of the preloaded bit would be an indicator of how many data bits had been shifted in. Perhaps the hardware could be modified to preset the shift register on a read... -michael ******** Note new website URL ******** NadaNet and AppleCrate II for Apple II parallel computing! Home page: http://home.comcast.net/~mjmahon/ "The wastebasket is our most important design tool--and it's seriously underused."