May not be brilliant programming but it shows a working system. http://cottageworker.com/wp-content/uploads/2014/05/
system4
System-4 Bus
The system bus card is built from VERO board and uses SIP style sockets and Radio Shack card supports. Each system card connects to the bus with a right angle single row header at the bottom of the card. At the back of the picture is the original power supply everything, is mounted on a […]
System-4 CPU/1861 Video/Keyboard Card
This a combined CPU/Video/Keyboard card. The right side of the card is the basic 1802 and support circuits. The bottom left contains an 1861 video subsystem and the upper left contains the parallel keyboard interface. This card was made obsolete by a new 6845 based video card. http://cottageworker.com/wp-content/uploads/2014/05/
System-4 6845 Alpha Numeric Card
The video card is based on a 6845 circuit from the May 1979 issue of Byte magazine. The circuit uses a 6116 2Kx8 Ram and provides dual port access to the RAM for both the system bus (circuit on the right) and video generation (circuit on the left). The circuit does not wait for horizontal […]
System-4 CPU Card
The system card is a fairly standard 1802 setup. A circuit remaps the 4K EPROM from the bottom of the address space (0x0000) to the top (0xF000) after the first access to an address in the upper block following a system reset. The circuit on the lower left side of the card replaces the original […]
System-4 Memory Card
This is the top view of the 24K memory card, only 16K is populated. The jumpers on the card are for setting card location within the address space, the need for more memory never materialized. http://cottageworker.com/wp-content/uploads/2014/05/ The Bottom of the memory card. Back then building a computer was a little like knitting a sweater, the […]
System-4 Front Panel Card
The I/O card has the requisite 8 switches and LEDs connected using a pair of 1852 chips and using the N2 I/O signal. The single LED at the top is connected to the Q signal and the lower switches are connected to the Reset/Run and EF4 lines. http://cottageworker.com/wp-content/uploads/2014/05/
System-4
This is the last of several 1802 based systems I built between 1978 and 1983. This system like all “real” computers has a system bus and separate Front Panel,CPU, Memory, and Video cards. The original system used an Apple parallel keyboard that was damaged many house moves ago. Last year the system was modified to […]