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Old
Computer
Hardware
My first computer was based on the COSMAC ELF design which appeared in Popular
Electronics, back in 1976. It used an RCA 1802 CPU and had
all of
256 bytes of RAM. I modified the design by adding a hex keypad (instead
of toggle switches) and a different hex display.
My final 1802 design (in 1980) had 4K of RAM, an ASCII keyboard and a simple video display based on the Motorola MC6847 (used in the first Radio Shack color Computer). At about this time, I realized that I had learned all that I could from the 1802, and it was time to move on to a more mainstream processor. I looked at the 8080 and Z-80, but just didn't like the instruction set and in the case of the 8080, the need for multiple power supplies. I also looked at the Motorola 6800 and found both the hardware design and instruction set to be simple and elegant. The 6800 appeared to be out of my budget, until I found one on sale for $3.50.
My first 6800 system was finished in late 1980, and I quickly moved on to the 6809 - probably the best 8-bit processor of all time. My first 6809 design was on an SS-50 bus wire-wrap card. It had 64K of DRAM, a Signetics video chipset and used an SS-30 (the SS-50 I/O bus) floppy disk controller to boot the Flex OS.
This machine was huge - 12 slot SS-50 motherboard, steel case, huge linear power supply and a surplus open frame monitor. It was quickly replaced by a new 6809 design based on the 6883/74LS783 SAM address translator IC. The 6883 was at the heart of the Radio Shack Color computer, providing DRAM address multiplexing and I/O decoding in a single 40 pin IC and supporting the 6847 graphics display IC. My design used it only as a DRAM referesh/address multiplexer and I/O decoder. The design had 64K of DRAM, a 6551 UART providing two serial ports (for my small Heathkit terminal and a modem) a parallel port and a double sided/ double density floppy disk controller. I used the Western Digital WD 1770 (a 28 pin device) a data separator IC and bits from the 6821 parallel port IC to provide the side select. The whole computer was wirewrapped on a board that fit on top of a 5.25" floppy, with room to spare.
My final 6809 design used 64K of static RAM and ran at 2MHZ. It used a 68681 dual UART for communications, and the WD1770 FDC describled above. The card fit on a 3" x 6" wirewrap board.
My final 1802 design (in 1980) had 4K of RAM, an ASCII keyboard and a simple video display based on the Motorola MC6847 (used in the first Radio Shack color Computer). At about this time, I realized that I had learned all that I could from the 1802, and it was time to move on to a more mainstream processor. I looked at the 8080 and Z-80, but just didn't like the instruction set and in the case of the 8080, the need for multiple power supplies. I also looked at the Motorola 6800 and found both the hardware design and instruction set to be simple and elegant. The 6800 appeared to be out of my budget, until I found one on sale for $3.50.
My first 6800 system was finished in late 1980, and I quickly moved on to the 6809 - probably the best 8-bit processor of all time. My first 6809 design was on an SS-50 bus wire-wrap card. It had 64K of DRAM, a Signetics video chipset and used an SS-30 (the SS-50 I/O bus) floppy disk controller to boot the Flex OS.
This machine was huge - 12 slot SS-50 motherboard, steel case, huge linear power supply and a surplus open frame monitor. It was quickly replaced by a new 6809 design based on the 6883/74LS783 SAM address translator IC. The 6883 was at the heart of the Radio Shack Color computer, providing DRAM address multiplexing and I/O decoding in a single 40 pin IC and supporting the 6847 graphics display IC. My design used it only as a DRAM referesh/address multiplexer and I/O decoder. The design had 64K of DRAM, a 6551 UART providing two serial ports (for my small Heathkit terminal and a modem) a parallel port and a double sided/ double density floppy disk controller. I used the Western Digital WD 1770 (a 28 pin device) a data separator IC and bits from the 6821 parallel port IC to provide the side select. The whole computer was wirewrapped on a board that fit on top of a 5.25" floppy, with room to spare.
My final 6809 design used 64K of static RAM and ran at 2MHZ. It used a 68681 dual UART for communications, and the WD1770 FDC describled above. The card fit on a 3" x 6" wirewrap board.
Pictures
From the Planes of Fame
Museum
Me-262:
Photos taken August 29, 1995 with an Apple Quicktake 150.
Photos taken August 29, 1995 with an Apple Quicktake 150.