Vermes
Advanced Member level 4
It is a copy of microcomputer Cosmac Elf. This construction was described in article here:
LINK.
Cosmac Elf is a simple construction based on microprocessor RCA CDP1802. There is not a ROM with monitor, so entering the program is via system DMA built in the processor into the RAM. Its capacity is only 256 bytes. You can enter data using 8 switches giving a single byte in binary code. It is not possible to jump to the specified address, so if you make a mistake, you must set the control switches LOAD and MP (memory protect) and „click” the right amount using the button IN. Hexadecimal display operates in snap mode, so the current state of switches is not displayed. It is displayed after entering the data to the memory. The display can also be used to show the memory content during viewing and is available from the program. There is also a LED.
The microprocessor has several inputs, which can be tested by the conditional statements, several outputs selecting I/O devices and one bistable output controlled by its own two statements (on/off). Address bus is multiplexed. Programming in machine language is very convenient, because usually you need to give the number of register, data or address next to the number of statement (5N, 30 NN type, etc.) and you do not need to encode anything binary and then change into hexadecimal.
Panel with switches is made of aluminum. Descriptions are accidential, because after etching in NaOH and brushing, the board covered with dark green raid. After application of the dry decal in the appropriate places, the raid was etched in phosphoric acid. Slats are made of stained and waxed pine.
In addition to the original construction, there is a resistor pulling to line /MWR, stabilizer 7805 instead of LM309K and display TIL311 instead of HP 5082-7340.
Pictures:
Link to original thread - Mikrokomputer Cosmac Elf