Dietz Mincal 523
| Manufacturer: | Dietz Computersysteme |
| Type: | Mincal 523 |
| Year: | 1971 |
| Technology: | TTL, transistors 8 kwords core memory with 19 bits (+1 parity bit) 1280 words ROM for microcode and loader |
The Mincal 523 is quite an exotic computer from today's point of view. Only the word length of 19 bits is unusual, but is has to be noted that this computer was designed for process control and processing of BCD values was normal. Of the 19 bits the top bit is the sign, so the remaining 18 bits can represent 4½ BCD digits (from 0 to +/-39999).
The exceptional design of this computer was revealed only little by little during the reverse engineering (there was practically no documentation and all schematics had to be drawn and recreated by hand). The CPU itself is built simple. The machine consists of a lot of circuit boards with low integrated TTL ICs, three of the boards form the processor control, one contains the ALU and six are for the hardware registers A-F. The remaining boards control the interrupt and level logic as well as the I/O section.
Nonetheless the computer's abilities are very powerful (but not particularly fast). This is achieved by micro programming that saves a whole lot of hardware effort at the cost of speed. The special about this, however is that the micro program is located in the normal address space of the CPU. It is realised in form of foil ROMs (see beneath) and is accessed automatically during an instruction fetch. The opcode of the machine instruction is used to form the jump address within the microprogram ROM. But it's also possible to write own microprogram routines and put them into core memory. There is an instruction to call a microprogram routine from core memory and continue execution with normal instructions afterwards.
History
The firm Dietz is known amongst computer firms mainly with the very successful system 621, intoduced 1971. Initially the company, created 1951 by Heinrich Dietz, developed and built electronic assemblies for the industry. They gradually moved from analog to digital electronics. So they were in best company with other firms like Digital Equipment or Hewlett Packard who also started with process control or measurement equipment and who only lated jumped on the computer train.
- 1951 Formation of the company DIETZ Instustrie-Elektronik
- 1957 Launch of digital technology with the relais operated measurement system ZDE
- 1962 The ZDE is replaced by the transistorised system COMBIDAT
- 1965 Introduction of the MINCAL series
MINCAL 3: free programmable BCD computer
MINCAL 0 and MINCAL 1: fixed-program computer (with diode matrix)
Around 50 machines were built according to statements of the company. - 1967 Draft of the MINCAL 4
This computer should have a word length of 25 bits, but development was stopped early due to high costs. The problem was that core memory with 26 bits (including a parity bit) would become terribly expensive. - 1968 Introduction of the series MINCAL 4 with the models 4E and 4N
As a compromise the MINCAL 4 was built with a word length of 19 bits. The core memory from Valvo was now noticeably cheaper.
Quality control with MINCAL 4N - 1970 Introduction of the MINCAL 5 with the models 523 and 513
- 1971 Introduction of the MINCAL 621 (later renamed to DIETZ 621)
Dietz had a cooperation with the French firm Télémécanique, who sold the MINCAL 621 in France as T621.
Conversely the Télémécanique T1600 was marketed as MINCAL 1600 (and later DIETZ 1600).
mincal 621 (year 1975) with "dietzdisk" and card reader - 1976 Introduction of the dietzdisk as cheap mass storage device,
somewhere between a floppy and removable disk drive.
dietzdisk alias Dynastor FX300
The ROM of the Mincal 523
ROM module of the Mincal 523
Top view: One can see 8 words with 19 bits each. Such a board set contains up to 64 foils with 8 words at 19 bits each, i.e. 512 words in total.
Closeup of nine bits
Each copper curl corresponds to a primary winding of a transformer whose core consists of the vertical ferrite rod. If a current pulse is sent through a copper trace a current is induced in the secondary winding (located below the yellow insulating foil) of the transformer. Accordingly no current is induced in those cores where the copper trace just goes past the core.
The cores that read out the bits
The paper-thin circuit foils from the side
32 foils each are located above and below the top epoxy board. Thus the aforesaid transformer has 64 primary windings.