There was not much progress the last months, mostly because of a new project that I hope to show soon.

I have new ideas now about the distribution over several pcb's. Each pcb will have a DIN41612 96-pin connector to a backplane. For several subsystems, it is very easy to get over 96 signals, so reshuffling was needed. Also there is a limit to the number of relays that will fit on a pcb, the maximum is now 40. The size of the pcb's will be approx 10 x 14 cm.

1. The register pcb implements 4 registers of 8 bits (32 relays). Of this pcb, 4 will be needed to implement the 7 16-bit registers (not all parts will be placed).
2. The PC and decoder pcb. Implements 6 bits of the program counter (3 relays per bit), and circuits for decoding the registers. Two of these are needed for a 12 bit program counter, the decoder parts are not needed on the second pcb.
3. The ALU pcb implements the 8 bit ALU, with both input registers A and B included. Two pcb's are needed for the 16 bit ALU.
4. Instruction decoder
5. Memory card. Two are needed, one for the program memory and one for the data memory. Includes the data shifter.
6. The backplane will have connectors for all mentioned PCB's, and will hold the displays and buttons for the calculator. There will not be a straight 1-to-1 wiring of all connectors, every card will only work in its own position on the backplane.

For pcb's 1,2 and 3 I did put complete schematics in the Hackaday file section. The PCB design is almost complete for registers and pc/decoder, and halfway for the ALU.

The instruction set was again changed. Only half of the registers had logic instructions, this turned out to be impractical. Now, all registers have the same instructions. The price to be paid for this was that conditional instructions are now only for the PC and not for other registers (The ARM-like conditional instruction were not needed so much). In the Hackaday file section, the architecture and instruction list were updated. (My doc-to-pdf converter has trouble with the lines around tables, sorry about that).