I worked out a method to inject the proper signals to test out both reading and seeking operations of the emulator role, using loopback from diagnostic output signal ports back to the relevant input pins. Although it was my day to join the 1401 Restoration team at CHM, in the late afternoon I coded up the mechanisms to produce the signals that an Alto would.
When slide switch 2 is turned on, with the emulator board attached, the emulator testbed will loop back SelectUnit1In and ReadGateIn which will cause SectorMarkOut, SectorNumberOut, FileReadyOut and Ready2ReadWriteSeek to be generated if a virtual cartridge is mounted on the emulator.
If I push button2 while a virtual cartridge is mounted and switch 2 is on, it will trigger a sequence of loopback signals to drive a seek. That is, the loopback will deliver TrackNumberIn and StrobeIn. If the emulator responds correctly, I should see AddressAckIn and Ready2ReadWriteSeekIn respond, with the new cylinder value I injected in TrackNumberIn appearing on the seven segment displays.
Independently, I will loop back HeadIn based on switch (1) just to verify that the Head value in the seven segment displays changes appropriately. I don't have an easy way to test writing to the emulated disk, especially to update some but not all records of a sector.