2764 EPROM emulator

The emulator enables a Type 2764 EPROM in an existing circuit to be replaced by a static RAM. It is a very compact circuit: together with Hie stand-by power supply, it fits on a 105×40 mm (4 1/8 x 1 9/16 in) board.

To all intents and purposes, the action of the circuit is indistinguishable from that of an actual 2764 EPROM. The programming voltage may be 12.5 V or 21 V. An additional advantage of the emulator is that programming and erasing are not necessary during a development phase, thus saving much time.

The position of switch S2 determines whether the circuit is actuated or inactive. When it is closed, the circuit is inactive and the memory cannot be influenced externally: it is then in the standby mode. This mode should be selected when it is expected that the circuit will not be used for some time or when it is removed from. or placed into, another circuit.

When S2 is open, the content of the memory is protected by IC2, T4, and T1. The only way the memory can be erased is by placing it in an EPROM programmer, setting the switch S1 to erase and actuating the function ‘Blank Check’ or ‘Read Out’ on the Programmer. When this routine has been completed, the entire content of the 101- is set to FF-H. Switch S1must then set to positions ‘program’ again, whereupon the emulator can be programmed in 11 traditional manners.

When programming has been completed., S2 must be closed and the emulator can then be inserted into its proper place in the circuit. Before that circuit can be operated S2 must be opened again.

The battery supply is switched on and c with switch S3: when it is switched, off the content of the RAM is lost, course. As can be seen in the photo, tWO PCB tel minal strips with extra long pins are used to replace the EPROM pins.
Parts list
Resistors:

R1, R8 = 22 kΩ
R2, R15= 100Ω
R3, R4= 560 kΩ
R5, R11= 68 kΩ
R6= 39 kΩ
R7= 3.3 1kΩ
R9=330 kΩ
R10= 560 kΩ

2764 EPROM emulator Schematic diagram

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