And yet another preview.
PS. The 16 bit computer nor windows ,has not crashed yet running the 99 bottles of beer program.
That is good sign that the 20 bit computer will work. I expect to have the ALU and memory board finished soon
as I have to tack on just the new bits, the old lay out is the same.

Finished the ALU card. Memory cycle is 1.6 uS. Repaced the
PAL with TTL.

A TTL CPU with core memory sounds awesome, do you have any PDF's of the circuit and block diagram we could have a look at ?

Sid

Sorry by it is just emulation, of core for timing. if core stacks were around it would be easy to interface as it is designed
around the read/write back memory cycle.


The best example may be the PDP-8 /E schematics.
They use a 20 MHZ clock to generate core timing logic. strobe here, pulse there, latch now.

The other two PCB's are out the door. Since a long weekend is coming up I will relax before summer ends.
I have all the parts, to build the PCB's for early September.

I got the hamsters running at full speed. Testing with 1.33 uS memory cycle.

Set the default speed to 1.5 uS, like the PDP 9/L (1969-1970)
Expected use of MSI TTL like the 74181 has the 16 bit cpu for late 1970
and the 20 bit cpu for 1971 release dates.

The SPI interface did not work, but I reprogrammed the 22v10 for a simple bit bang interface
with the 74hct299.The code now works to initialize the SD card, -1 no card 0 card.
Testing of a sector read/write is the next project. A greater than 4 Mhz clock is needed for it
to work. < 2.0 uS.

Revised the order code yet again. Addressing modes are R ,+-R,R+-,R]
Need to revise the software with the new changes.
The PCB's are IN, so I am almost ready to start building.

The PCB's are mostly finished. I just need to port over the programmable logic from the 16 bit computer to the 20 bit CPU.
I need to take out the trash and stock up on more Cola and Pizza,before I can get back to work.

The supermarket hid all the pizza's and high caffeine products. I have got the basic bootstrap loader working
but the text io routines need work as well as the test program.
A) ADD 1+2 -> 3 : pass
B) HALT : pass
C) CATCH ON FIRE : fail

As it may have looked in 72.
Now a working 20 bit computer with just serial IO.

Nice sepia effect. Well done on getting a good exposure for the LEDs too. All looks good!

Revised the order code from HEX to octal. The front panel will be 7 octal digits, 7 segment displays for now. Nixie tubes
later perhaps. Added back few features I had to drop for testing.
Other than indirect addressing I am happy with the layout of the opcodes.

Have the first draft of the bios finished. No named files,but Mag Tape style I/O. 512Kb max file size per tape.
8K words for I/O buffers. 8K for stack of hidden memory.

Now that I have a OCTAL computer of 20 bits, I need a octal Front Panel and new mother board.
The mother board will have a jumper for a 20 or 21 bit system.
Led will be Green if running, Red if stopped and Black when off.
Will use a 74H04 rather a 7404 in the original circuit.
PS: The gerbers are out the door.