EDDA 3 - Data Address Space

Parent Category: Articles Category: EDDA 3 - An Early Transistorized Process Computer Written by Administrator

The data adress space is called "Adressenplan" = "address layout". In the basic data address space there were 100 addresses. Not much were memory, most had special functions. Data values always have a width of 4 decimal digits. Some address access registers of memory managment or the processor, this resembles to Microchip's  PIC 1640 architecture.

Addresses

Function

0 to 2

Constants: 0, 1, and 1000

3, 4

Shift register, implemented by a special, double wire wrap core memory. A value being written to address 3 turns up at address 4 shifted to the left by one decimal digit, and vice versa.
Important for multiplication or division.

5 to 34

General core memory: 29 four-digit numbers

40

Input: external on/off switch, represented as 0000 or 0001

41 to 49

Four-digit input channels, depending on the equipment

50

Instruction number = "program counter". Only the two lower digits 00 to 99 are valid (corresponds to the "PCL" register of the PIC1640 microcontroller).

51

The two upper digits of the "program counter". Needed if the program memory is extended to more than 100 cells. Basically it then operates with bank switching like the CS segment register of the 80x86 CPUs and it corresponds to the "PCLATH" register of the PIC1640 microcontroller.

60

Writing simultaneously deletes addresses 61 to 64.

61 to 64

Output channels with a decimal digit each

64

Double function: value for the index register on address 99
(corresponds to the "FSR" register of the PIC1640)

65 to 68

For expansion card "EDA1": 4x4 Nixie tubes

69

Dummy register. Serves as destination for calculation results that are not needed (for tests).

70 to 89

Reserved for expansion cards (see "Peripherals")

99

Index register. If the address "99" is used in an instruction, not the fixed memory cell 99 is read or written but the respective address is fetched from memory cell "64" (corresponds to the "INDF" register of the PIC1640).