Cactus: 6502 Homebrew Computer
The Project:  Motivations  Specifications  Current Focus  
              Front Panel Logic  Cards
Events:       VCF East XIII  VCF West XIII  DEFCON 26  VCF Midwest 13  
              VCF East XIV  VCF West XIV  VCF Midwest 14
The Future:   Want a Cactus?

List Of Cactus Cards

Photo Name              Description Date Built      Disposition
address debug Address Test/Debug Card Mk I Provides buffers for the address bus to the address LEDs. Initially served as a way to hardwire the address and data bus, as well as see the data bus during early testing April 2018 In use
address control Address Control Card MK II Drives the bus when the CPU is not asserted. Allows user to manually load an address from toggle switches, or auto-increment addresses. Uses 4x 74193 counters cascaded together, and two 74245s to isolate this card from ths bus when the CPU is asserted. Was original the Mk I when it drove the front panel LEDs, but that function was moved elsewhere. October 2017 In use
data control 1 Data Control Card Mk I Provides scratch register for data to be read and modified before being deposited back into RAM. Buffered both on incoming and outgoing data. Based on an early design concept for front panel data flow (based on design revison 15? 17?) Requires 4 single direction buffers, and originally displayed the contents of the data bus when the CPU was asserted. Had major stability issues, and was incredibly tedious to build. September/October 2017 Retired, non-functional
data control 2 Data Control Card Mk II Provides a scratch register for data to be read and modified before being deposited back into RAM. Buffered both on incoming and outgoing data. Major upgrade for data bus control. Allows integration with the Front Panel I/O card for additional logic to govern CPU interaction. Significantly improved stability, and reduced part count. April 2019 In service
front panel io Front Panel I/O Card Mk I Allows the CPU to interact with the data control card, so that data switches can be read by software. Provides buffer for data bus, originally served by Data Control Card Mk I. Provides data latch for software-controlled LEDs. Effectively replaces all of the Data Control logic due to increased complexity. May 2019 In service
status control Status Control Card Mk II Contains the state machine that controls front panel operations. Sequences all front panel opertions and debounces all momentary switches. Original Mk I variant had no switchpress lockouts, and would either miss momentary switch commands, or had sequences pulses that were too long. Additional lockout latches ensured single-pulses for Examine, Examine Next, and Deposit Next operations. Status Control is in charge of the Data Control Card, Address Control Card, and Front Panel I/O card. It also controls if the CPU is running, provides debounce for the step switch, and allows the RAM to be write-protected (write protect likes to randomly activate) March 2018 In service
led board LED Card Mk I A passive card to provide software-controlled data LEDs, and a dedicated array of data bus LEDs. Spring 2019 In service
cpu 1 CMOS CPU Card Mk II WDC65C02S CPU, clock circuit, and reset supervisor. Original Mk I CPU card was, modified to add in improved single step operation. Worked for awhile but eventually broke. March 2018 Retired, non-functional
cpu 2 NMOS CPU Card MK I NMOS CPU card intended for an original MOS6502. Provides buffers for address and data buses, as well as essential control signals, and a reset supervisor. Requires NMOS CPU speed module to be installed to determine clock speed. June 2018 In service
cpu 3 CMOS CPU Card Mk III Second attempt at a CMOS CPU card. WDC65C02S CPU, clock circuit, data bus buffer, control logic, and jumpers for interrupt disable. April 2019 Unused, never really worked well
cpu speed modules NMOS CPU Speed Modules 50KHz module divides CPU clock by 20, intended for use with the MOnSter 6502 but works with standard NMOS CPUs. 6502 module buffers control signals to the bus, does not modify CPU clock. Summer 2018 In service
ram RAM Card Mk II First card for the Cactus constructed. Provides 32K SRAM, 2K NVRAM. Has faulty Memory Protect logic, which has been disabled by an on-board switch. Modified from the RAM Card Mk I, which lacked NVRAM August 2016 In service
feram 8K FeRAM Card Mk I I wanted to see if I could build one. Never got the Phi2 qualification logic right for this type of RAM March 2020 Unused, does not work
rom ROM Card Mk I Accepts 27XX EPROMs or 28XX EEPROMs in 16KB or 32KB sizes. Provides jumper to select upper or lower bank on 32K ROMs as only 16K is available to the bus at a time. September 2017 In service
serial 1 Serial Card Mk I MC6850 ACIA provides serial interface. Jumpers allow baud rate selection between 38400 and 75 baud. Originally planned as a dual-serial card, ran out of space. March 2018 In service
serial 2 Serial Card Mk II Dual 6551 ACIA was intended to provide twin serial interfaces. Baud rate selection was done in software. Worked for only a few months before failing suddenly. Debugging efforts never did yield an answer. And no, I didn't populate it with the modern WDC65C51 chips -- I used CMD, CSG, Rockwell, etc. June 2018 Retired, non-functional
parallel 6522 VIA Parallel I/O Card Mk I Provides 16 bits of parallel I/O using a WDC65C22, but was maily used for driving 8 LEDs. That functionality is now provided by the Front Panel I/O card, with the intent of freeing up the 6522 to do more. June 2018 Operational, rarely used
sound card Sound Card Mk I Phillips SAA-1099 sound card, does not include on-board amplification, but works surprisingly well. September 2018 Operational, rarely used
glitchbus adapter Glitchbus Adapter Mk I Intended to provide interaction with Glitchbus peripheral cards from Glitchworks March 2020 Unfinished
bus 1 C-35 9-Slot Bus Mk I The first piece of the Cactus ever built, from before I knew what I was going to build with it. Provides 1K termination on all address and data lines. Was deemed to small for regular debug work May 2015 Retired, used for card storage
bus 2 C-35 16-Slot Bus Mk I I wanted more bus slots, so I added more bus slots. I also put one at a right angle for debugging May 2019 In service

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This page was last updated on 6-8-2024

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