Peter Lohmer CP/M Calculator

Peter Lohmer built the computer in 1978 - 1980 during his studies at the University of Applied Sciences Cologne at the Department of Communications Technology. A modular design based on the then quite widespread ECB bus is used. At the heart of the computer is a Z80 CPU card with 4 MHz clock frequency. The computer has 64 KiB dynamic RAM. Memory was at that time almost unaffordable for a student (64 KiB about 5000 DM). The dynamic RAMs come from a mainframe that was converted at that time. The floppy controller with DMA (Direct Memory Access) serves the two 8 inch floppy drives from Shugart. A Kansas City interface for storing and reading data on a conventional cassette recorder was needed during the development period until the drivers for the CP/M were developed. The binary data is stored as 9600 Hz or 4800 Hz tones.

The CP/M operating system has 56 KiB memory, the other 8 KiB use the BIOS and system internal functions. A second Z80 CPU card with a connected 512 x 256 points graphics memory serves as a terminal replacement. Thus 25 lines with 80 characters can be displayed.