Big news. First prototype was a disaster. This one may be too.  Only the motherboard PDF schematic is included and that is still incomplete, as I did not implement (yet) the logic for talking to the peripherals.

So this is how the system work:

- one interface to talk to the drive  - to make it believe it's talking to the mainframe;

- one interface to talk to the mainframe - to make it believe it's actually talking to the tape drive;

- one bidirectional buffer interface to separate the microcontroller from the previous two (you will see why later);

- one SRAM memory buffer interface. The board also contains one microSD card and some serial communication stuff (max232, usb serial) for some LCD and some PC terminal monitor/debug.

Later additions - this is why I made it modular:

- one SCSI peripheral interface;

- one ESDI / MFM peripheral interface;

- other stuff, depends how many spare pins I have left.

The microcontroller belongs to STM32F4 family. 

Here's the trick:  the system can be set on "bypass" allowing the drive to talk to the mainframe while the STM32 listens and logs the protocol - which is a real sadomasochistic pain to implement and understand;

Tape can be read and dumped to SDCARD. Also a new tape can be written from the SDCARD.

Mainframe can talk to the SDcard while the tape stays offline;

sdcard becomes an USB peripheral so the files can be inspected, or a SCSI peripheral, or an ESDI/MFM storage device for old equipment;

The 9 track tape drive can also become an USB peripheral - a big, nasty, noisy useless USB storage device. Or a SCSI peripheral. 

See attached pictures and the PDF schematic here.

As always - WARNING:  do not try to reproduce, this is an incomplete work in progress and there may be mistakes.  

 Mainboard schematic is here.