The first is based on a piece of gear I bought many years ago at a University auction. It is MacLab MKIII. Research indicates that this went on the market in 1988. The date codes on the chips in my unit are 1992.
This thing was intended to be connected to some ancient Apple computer via a 50 pin SCSI cable! Inside is an NCR 53C80 chip to handle the SCSI. I have essentially no interest in this aspect of the device.
Amusingly, a Google search turns up my pages from long ago.
I somehow managed to disassemble the rom and did a fair amount of annotation. The ROM is/was an AM27C256 (32Kx8), but only 16K was mapped into memory. Thus the rom was divided into a first and second section. The second section had content, but pin 27 (A14) was permanently wired to ground, so only the first section would be seen by the 6502.
The box has four analog inputs and one analog output. Each of these gets a pair (marked + and -) of BNC connectors on the front panel. This analog IO is the only reason I would want to fool with this device.
The back has several interesting connectors:
No analog input on the back connectors (unless it is hidden along with the analog output signals).
What could that i2c bus connector be all about?
A rule with this company seemed to be to choose the most unexpected and inconvenient connector possible for each function.
The inside is more interesting. There is a logic board and a separate analog board.
Here is a chip list from what I call the logic board:
R65C02P4 - the 6502 cpu HY6264 -- 8K of static ram HY62256 -- 32K of static ram rom socket -- hopefully I have the ROM somewhere. R65C22P4 - one VIA chip (pio) R65C22P4 - another VIA (pio) MC68B50P - ACIA uart -- serial port ADS7800JP -- Burr Brown - 12 bit single channel ADCThe two static ram chips give 40K of ram, and the rom uses 16K of address space. This leaves 8K to map peripherals. The R65C02 is a 6502 variant made by Rockwell. It is a low power CMOS part and adds several instructions.
The ADC has a 3 us sample time. It is odd that this part is on the logic board. The so-called analog board must only support the four DAC channels for analog output.
I could use some little STM32 board and splice in a USB interface. Or I could be really carried away and add some little ARM board and give it a network interface, using my Kyu operating system.
We don't necessarily need 40 IO pins to "emulate" the 6502. In fact we might find it better to tap into the circuitry on the board elsewhere than the 6502 socket.
But thinking for now about 6502 signals. We can eliminate power, ground, and pin 35, which is a N/C pin. I see three clock pins PHI1o, PHI2o, and PHI2 that we can probably ignore. This gets us down to 34 pins. If we don't care about accessing the ram and rom on the board, there are 3 address pins we can ignore (or tie high/low to indicate IO access). Now we are down to 31 signals. Other signals need to be evaluated case by case (as well as investigated on the MacLab itself.
Tom's electronics pages / tom@mmto.org