The Dage Scientific MC-3 is a simple microprocessor development system based on the 1802 processor. A construction article for the MC-3 was published in the April and May issues of Radio-Electronics magazine. I have the original articles torn out of my copy of Radio Electronics and the complete set of documentation that came with the system including both manuals. I built mine with the 16K EPROM and 8K of RAM and I added an extra port or two.
The MC-3 was available as a kit from Dage Scientific ($195), as a set of PC boards that you could purchase and populate yourself ($35), or you could build the whole thing from scratch using the PC artwork printed in the magazine. A copy of the EPROM containing the operating system/monitor was offered for $10, or you could program your own EPROM using the monitor source code in the magazine.
The main part of the MC-3 is a pretty bog-standard 1802 implementation -- CPU, memory, address latch, I/O decoder. The first 16K are occupied by an EPROM that contains the operating system. The rest of the memory space can be occupied by either RAM or EPROM. The board is socketed for 16K chips, but there is an extra pad that enables you to stack two 8K RAM chips in one socket, wiring the high bit of the address bus to the opposite signal. The operating system required RAM in the high bytes of the address space, so one 8K RAM is located at M(E000).
One of the sockets has a header next to it for a daughter card that turns the socket into an EPROM programmer. The daughter card stretches the write cycle so that an EPROM has enough time to write the data before the next write cycle. The power supply for the MC-3 included a 12-volt line for programming EPROMS, and there is a memory move routine in the operating system for copying a program from RAM to an EPROM.
Six of the seven I/O ports (I/O 2 through 7) are brought out to an edge connector that you can use to bring signals to the breadboard on the top of the system -- the MC-3 was intended as a development system for microprocessor-controlled projects -- where you wired up your project and worked on your program. The seventh (I/0 1) is used to read and write the serial interface to the keyboard/display console.
The front panel is different from the normal ELF model. Rather than switches or a keypad wired to DMA or an input port, it's connected to the main system by a telephone cord. Data is sent to and from the front panel using a set of shift registers and the Q line as a clock. There are six 7-segment LEDs in the display, and a 16-key hex keypad with 4 function keys for data input. Each segment of the LED is individually addressable, so you could form words ("HELP" is popular) or send digits.
The operating system/monitor offered the standard Write, Examine, and Execute commands. It also had a debug mode that enabled you to enter breakpoints via the front panel and then examine the memory and registers. The SCRT is included as part of the monitor, which also includes the following subroutines.
- GetKey: Places the value of the last key pressed in the low byte of R(A).
- Hex2Seg7: Replaces the hex digit in the high byte of R(A) with the 7-segment code required to display the hex digit. It reads the pattern from a table of values located from M(0080) to M(008F).
- DispMem: Outputs six bytes starting at a specified address to the display.
- 9Decode: The value of R(9) is decoded from four hex digits to four 7-segment output codes, along with the contents of the memory location pointed at by R(9). The value is prefixed with “A-“.
- QClk: Uses SEP for call, returns to R(3). Cycles the Q output line 8 times to clock a byte from the main board to the keypad/display console.
There were also a couple of utility programs.
- ROMtotal: Totals the value of all bytes in a section of memory so that you can compare copied bytes, etc.
- BulkMove: Moves a specified block of memory from one address to another. Typically used to program EPROMs by moving bytes from RAM at M(E000) to the EPROM at M(8000).
The monitor EPROM is located at M(0000), so it runs as soon as the system is turned on. There is a section of code right at the beginning of the OS that checks to see if the front panel is connected, if it isn't the monitor jumps to M(E000) and attempts to run the program at that location. In the basic MC-3, M(E000) is RAM, so it enabled you to jump directly to your program after reset, if you had a program loaded in RAM, or if you had put a custom EPROM in that socket.
The OS does not take up an entire 16K EPROM -- it only takes 5 pages. I copied the OS from the original EPROM to a new one, then put the original away and started adding my own routines to the EPROM. I remember that I put some 16-bit math routines in there, and one for reading from an ADC.
The documentation for the MC-3 consists of
- Assembly & Operation Manual for Model MC-2 Microprocessor Development System – Assembly instructions, operating system/monitor instructions, a detailed circuit description, and schematics for the system.
- Crash Course on Microprocessors – Programming the 1802 – Offers a general introduction to computers and computer programming, and then specific instructions for programming the 1802 and the MC-3 system.
- Photocopied pages out of the RCA Manual for the 1802.
- A manual programming form for hand assembly of programs.
The case for system says MC-3 on it, but the documentation and the article in Radio-Electronics both list the system as an "MC-2." Interestingly, the picture in the magazine article shows that the case says "MC-3."
The MC-3 was not sold as a "micro-computer trainer," but as a "micro-computer development system," the idea being that you would create your project with the MC-3, and then move it to the actual hardware once you had the project running. I don't know if any products were developed with an MC-3, but I rather hope that they were.
The MC-3 was also one of the last, if not the last, 1802-based project that I saw in the hobbyist press, at least until the ELF 2000 came around. I remember that Radio Electronics published an 1802-based model rocket altimeter and a Christmas tree light controller some time around then. I'll need to dig through the stack of articles that I tore out of my Radio-Electronics magazines -- I know that those two projects are in there somewhere. After that, the 1802 pretty much disappeared.
I talked to Dave Dage about the system when I ordered it -- basically making sure that I understood what I was getting in the kit and what I needed to buy. I remember him being quite helpful. I've tried to find Mr. Dage on the Web, but haven't been successful, yet. I'd like to make the documentation for the MC-3 part of the collection on the Yahoo group site, but want to get his permission first. I used the MC-3 for a couple of years, and lost interest in electronics and microcomputers for a while -- read that as "we had a baby and I didn't have time anymore." I have more time for playing now, so my MC-3 is one of four 1802-based systems that I have.