docs or software for Quay 900 (uses Quay 90F/MPS board)

I figured out the port and bit assignments for the Quay MPS-90F console serial port. Input from port 0 reads a receive character (and clears the data received flag), output to port 2 transmits a character, and reading port 1 gives the UART status, with bits 0 (LSB) to 4 being parity error, framing error, overrun error, data received, and transmit buffer register empty, respectively, all positive logic (1 is true). Switched 3 through 6 of the DIP switch are the baud rate, which is provided by a 4702 BRG chip and not the CTC as I'd previously imagined. Switches 3 through 5 off and 6 on gives 9600 baud. Don't yet know what the CTC is used for. Possibly for the SIO daughtercard, though there's no continuity directly from the CTC output pins to the SIO clock input pins. Contrary to my previous guess, the SIO daughtercard is soldered into what appears to be a Z80-PIO footprint on the main board; apparently when designing the MPS-90F they expected to need a lot of parallel I/O and not so much serial. I programmed an EPROM with code that prints "Hello world" then echos the each input character plus one, so that sending in "HAL" results in output of "IBM". That seems to work fine. I started writing my own monitor, inspired by the Apple II monitor, because I couldn't find a Z80 monitor I liked that would fit in a 2708 (1KB). The monitor works fine running in a slightly modified version of z80sim from z80pack, but fails on the real thing, sometimes hanging after the command prompt, and other times echoing the first received character endlessly. To misquote Sark, "Bring in the logic analyzer!"