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update README with new info about compatibility

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@ -23,14 +23,28 @@ Due to the dearth of documentation on the DCD protocol (see below), the protocol
namely read, write, and device identification. Responses to other commands are faked. Fortunately, this seems to be enough for the
device to function properly, including formatting.
The disk drive interface relies on use of the phase lines to read and write one-bit registers. Because the microcontroller mimics the register set in code instead of programmable logic, it has a response time that is, in the worst case, approximately one microsecond. This is not fast enough for Macs with faster processors to reliably detect that the device is present. As such, it can only be used on Macintosh computers with 8 MHz 68000 processors.
The disk drive interface relies on use of the phase lines to read and write one-bit registers. Because the microcontroller mimics the register set in code instead of programmable logic, it has a response time that is, in the worst case, approximately one microsecond. This interferes with the Mac's ability to detect that devices are present, since it expects effectively-instantaneous response time, and as a result, certain Macs are not able to detect devices beyond the first.
Compatible Macs:
* 512k (with Hard Disk 20 INIT)
Known Compatible Macs:
* With multiple devices:
* 512ke
* Plus
* With one device:
* SE
* Classic
* Classic II
Suspected Compatible Macs:
* With multiple devices:
* 512k (with Hard Disk 20 extension)
* With one device:
* Portable
* IIci
* IIsi
* LC (using internal secondary drive connector, if stuffed)
* IIx (using internal secondary drive connector) (requires nonstandard ROM)
* IIcx (requires nonstandard ROM)
* SE/30 (requires nonstandard ROM)
## Technical Details