Simulation and security device for data entry keyboard (5) of a computer (1), the keyboard including a set of row conductors (3) and a set of column conductors (4) which are electrically activated and arranged to provide a set of crosspoints, there being a set of selection keys (6) located at respective ones of said crosspoints for outputting electric signals of the row and the column conductors at the repsective crosspoints;
- the device comprising;
- an input-output unit (2) connected between the keyboard and the computer, a first memory (7) for storing an initialization program, a second memory (8) for storing a working program, a memorization assembly (9) for storing coded call instructions, and a switch assembly (10);
- and wherein
- the input-output unit furnishes scanning pulses to the row conductors of the keyboard, the computer is connected to said first memory and said second memory, initialization of said computer being accomplished by said initialization program, the working program being applied by said second memory to said computer subsequent to initialization of said computer in response to a transmission of a series of coded call instructions to the computer (1) via the keyboard (5);
- and wherein
- said memorization assembly (9) is connected to the input-output unit (2), the switching assembly (10) is connected to the memorization assembly (9) and to the column conductors (4) of the keyboard and to the input-output unit (2) to permit the transmission of the call instructions to the computer, thereby to prevent any transmission of coded instructions from the keyboard during initialization of the computer as well as the prevention of a transmission of the call instructions, the device permitting a subsequent transmission of instructions from the keyboard when all of the call instructions have been received by the computer;
- and wherein
- the memorization assembly (9) includes a command memory (11) containing the said call instructions as well as the coded addresses of these instructions, and an address counter (14) connected to the command memory (11);
- and wherein the security device further comprises;
- a pulse selector (23), and the address counter is connected further to a command output of the pulse selector (23) for receiving address command pulses from the commmand memory (11) synchronized with the pulses which scan the row conductors (3) of the keyboard (5);
- and wherein the switching assembly (10) comprises
- means (18) for reading call instructions, a switching circuit (16) connected by inputs to the means (18) for reading call instructions, the switching circuit (16) being connected to the command memory (11), to an output of the counter (14) and to the column conductors (4) of the keyboard;
- and wherein
- outputs of the switching circuit (16) are connected to inputs of the input-output unit (2), the switching assembly (10) furthermore including a comparator 19 connected to outputs of the input-output unit (2) to receive at each moment a keyboard row scanning code, the switching assembly (10) including means (20) connected to the comparator (19) for reading coded addresses of the call instructions, an output (21) of the comparator being connected to the means (18) for reading call instructions to command the transfer of the call instructions to the switching means (16) and to the input-output unit (2) when the code of the scanned row conductor corresponds to the code of the call instruction address, the switching means (16) being connected to the counter (14) for blocking any transfer of instructions coming from the keyboard (5) during the initialization and during the scanning of the addresses of the command memory (11) and of the row conductors (3) of the keyboard (5).