Viking QTO SCSI controller for QBUS

This board is a Viking QTO SCSI controller board for the QBUS. The board has an
onboard Z80 CPU, a Am33C93 SCSI interface circuit two Integrated Device
Technology FIFO chips, a DUAL UART and various interface chips and memories. The
board come in several variants for either disks or tapes or a combination of
both. Essentially these are all the same board using the same firmware but the
difference is the contents of the removable PAL (has been replaced with a
GAL16V8 on this board). I did try to find the company that once upon a time made
the card but it was quite dysfunctional at this time. There web page stated just
it not operating anymore. However I managed to get a mail to some person close
to the company but unfortunately they could not help out.

Viking QT0 SCSI board QBUS

The manual lists the various models and lists jumper settings used. But the the
method on how to reconfigure the board into something else is not mentioned. I
managed to trace the connections from the socketed PAL to other components and
got to the conclusion that the PAL is simply an address decoder with to output
enable signals. Either enable disk or tape. As it happened after posting about
my troubles with the card in a vintage computer mailing list I received a mail
with the full contents of the replacement chip.

This are the equations used

    ==== P16V8C Programmed Logic ====


CsrIsTape     = !(  A13 & !A12 & !A11 & !A10 & !A09 & A08 & !A07 & A06 & !A05 &
!A04 & !A03 & A02 & Jumper3 & Jumper4
                 #   A13 & !A12 & !A11 & !A10 & !A09 & A08 & !A07 & !A06 & !A05
                   & !A04 & !A03 & A02 & !Jumper3 & Jumper4
                 #   A13 & !A12 & !A11 & !A10 & !A09 & A08 & !A07 & !A06 & A05
                   & !A04 & !A03 & A02 & Jumper3 & !Jumper4
                 #   A13 & A12 & A11 & !A10 & !A09 & A08 & !A07 & A06 & !A05 &
                 #   !A04
                   & !A03 & !A02 & !Jumper3 & !Jumper4 ); CsrIsTape.OE  = (1);

CsrIsDisk     = !(  A13 & !A12 & !A11 & !A10 & !A09 & !A08 & A07 & A06 & A05 &
A04 & A03 & A02 & Jumper1 & Jumper2
                 #   A13 & !A12 & !A11 & !A10 & !A09 & !A08 & A07 & A06 & !A05 &
                 #   A04
                   & A03 & A02 & !Jumper1 & Jumper2
                 #   A13 & !A12 & !A11 & !A10 & !A09 & !A08 & A07 & A06 & A05 &
                 #   !A04
                   & A03 & A02 & Jumper1 & !Jumper2
                 #   A13 & A12 & !A11 & A10 & !A09 & !A08 & !A07 & A06 & A05 &
                 #   !A04
                   & A03 & !A02 & !Jumper1 & !Jumper2 ); CsrIsDisk.OE  = (1);

.

                         ==== P16V8C Chip Diagram ====



                                    P16V8C

                         +---------\       /---------+
                         |          \     /          | -----           |
                 Jumper2 |  1                    20  | Vcc
                         |                           |
                 Jumper3 |  2                    19  | !CsrIsDisk
                         |                           |
                 Jumper4 |  3                    18  | !Jumper1
                         |                           |
                     A13 |  4                    17  | !A02
                         |                           |
                     A12 |  5                    16  | !A03
                         |                           |
                     A11 |  6                    15  | !A04
                         |                           |
                     A10 |  7                    14  | !A05
                         |                           |
                     A09 |  8                    13  | !A06
                         |                           |
                     A08 |  9                    12  | !CsrIsTape
                         |                           |
                     GND | 10                    11  | A07
                         |                           |
                         |                           |                         |                           |
                         `---------------------------'

Here is the JED-file to use to program the GAL.

Now unfortunately this is not enough to make it a disk controller instead of
tape controller (which was I wanted). On board there is a small EEPROM that
store some kind of secret information that the firmware uses to configure the
board. My first trial to disassemble the binary code of the firmware failed to
solve the problem, but again the help from people on the net rescued me from
getting yet more gray hairs.

This board has a a firmware utility that let it to be configured using a serial
port which connects to two unused pins of the 50 pin SCSI connector. All this is
well described in the manual. What is not described is to change the
configuration of the board from disk to tape or vice versa.

To be able to do that one has to enter a secret three character code at the
firmware utility prompt: Z <CR> $   or zed carriage-return dollar

Then you shall be greeted by a "A=" prompt where you can enter different codes.

for QDT/UDT (disk and tape)

A=4080 B=1181 Model=QDT/UDT s/n=xxxx


for QTO/UTO (tape only)

A=0 B=1181 Model=QTO/UTO S/N=xxxx


for QDO/UDO (disk only)

A=4080 B=0 Model=QDO/UDO S/N=xxxx


for QDD/UDD (diskA diskB)

A=4080 B=4080 Model=QDD/UDD S/N=xxxx


for QDA/UDA (disk only with bootstrap)

A=4080 B=82 Model=QDA/UDA S/N=xxxx

This worked fine for me and but I only tested to reconfigure it as a QDT. My
firmware is a version 4.0. But there are also a 4.4 firmware as well. I haven't
tested that one though.