Introducing the COSMAC 2020 ELF

As explained in an earlier post, I have started a pure vanity build of an CDP1802 system, which does not fit what we normally do, but it is something I have wanted to do for a long time.

Some background: I have been fascinated with microcomputers since 1975 when the digital logic professor came back from a CA seminar with an 8008 system.  My career started in the Navy after graduation, but I wanted to keep up my EE knowledge so in 1977 I acquired an 1802 ELF.  That was followed by a complete rebuild into a system with 64K of memory, built in EEPROM programmer, multiply divide unit, composite video interface and much more.  It took me several years, since the navy kindly asked that I spend time overseas for long periods of time.   In those days the memory was composed of 1K x 1 SRAM chips that consumed 50mA each or 30mA for the low power version.  So I decided to build these in 8K wirewrap cards.  Designed an ingenious bus interface long before the ISA bus was around.  But an 8K card had 64 2102 chips on it plus some CD4000 glue logic.  The low power version consumed almost 2 AMPS.  To get to 64K was going to take 8 cards and 16A @ 5VDC.  So I found a large transformer, high current stud diodes and large capacitors to build a 30A @5VDC power supply.  Unfortunately I never took pictures of this monstrosity.  By the time I finished wire wrapping the first 8K memory card and managed to get it working, Hitachi, Sony and few others produced the HM6116 2K x 8 SRAM chips.  These consumed only about 40mA per chip and so 4 of these at 160mA replaced the entire 2102 at 2A.  By the time I installed some these, the HM6264 8K x 8 SRAM arrived and entire 2102 board was replaced with a single chip using 40mA.  The final incarnation is shown here with the main board removed from the custom case I built.

The design philosophy this project will follow is delineated here.
1.    Use as many LSI CDP1800 series parts as possible, at a minimum
    a.    CDP1802/1806 CPU
    b.    CDP1854 UART
    c.    CDP1855 Multiply/Divide Unit
    d.    CDP1869/1870 Video interface System (VIS)
    e.    CDP1871 Keyboard Interface
    f.    CDP1877 Priority Interrupt Controller (PIC)
    g.    CDP1879 Real Time Clock (RTC)
2.    All MSI type parts will be 74HC instead of the original CD4000 type ICs
3.    All glue logic will be contained in CPLDs to reduce space and increase flexibility
4.    Will use a PCB instead of wire wrap

Follow along as this project slowly progresses.