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This page is little about the various QBUS systems and QBUS boards that we have in our possession.

KD11-F / M7264

Start with the original LSI-11 CPU, KD11-F, that included 4 kW of DRAM memory.
M7264 / KD11-F CPIU board

The board is a etch revision D and have plenty of patch wires. The board is manufactured around 1975-1976. Unfortunately the board is not running. Using a logic analyser showed that the MICROM without label is not behaving well. Since replacement chips is very hard to find the idea is to use a MICOROM chip from an spare KD11-HA (M7270) board. But as it turns out the substrate bias supply has changed among the various chip revisions. This board uses -5.1 V whereas the newer board uses -3.9 V. Thus a small modification is needed to the board to get it working by adding a 3.9 V zener diode.

KD11-HA / M7270

KD11-HA / M7270 / LSI-11/2 CPU

This is the LSI-11/2 CPU board, also known as KD11-HA or M7270. The same M7270 but with the empty socket populated with a EIS/FIS MICROM is called KD11-NA. The schematics or print set for the KD11-NA / M7270 (MP-00563) is hard to find but is included in the print set for MNC11 (MINC11) at page 181. The print set (MP00495) for the almost identical KD11-HA is yet to be found.

MSV11-D / MSV11-E

Below is a MSV11-D (M8044) board that I long ago modified to support 64 kbit memory chips. It involved replacing all memory chips and also rewriting the contents of the decoding PROM. The manual is here and then also the print set with the schematics.

Modified MSV11-D board

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 ====


                         +---------\       /---------+
                         |          \     /          |
                         |           -----           |
                 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)


for QTO/UTO (tape only)


for QDO/UDO (disk only)


for QDD/UDD (diskA diskB)


for QDA/UDA (disk only with bootstrap)


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.