1-Mbit adaptor for EPROM programmer

The adaptor allows you to program the 27C1001 EPROM which has a capacity of 1 bit organized as 128 Kbyte x8. To be able to use the present adapter. your EPROM programmer must be capable of programming 512 Kbit EPRONis such as the 27512 or 27C512 (64 Kbyte x8). The adaptor programs the 27C1001 in two steps of 64 kbyte each, and is simply plugged into the 28-way (or 40-way) ZIF socket on your EPROM programmer. The 64 Kbyte block selection is effected manually with the aid of a switch.

The circuit of the adaptor has few surprises. Socket 1 connects the adapter to the EPROM programmer, while socket 2 accepts the 27C1001. The .PGM), an input of the 27C1001 is.actuated (i.e., made logic low) when the programming voltage, Vpp, on socket 1 exceeds the zener voltage of D4, and .cs» on socket 1 is held low by the programmer. The zener diode also enables the programming voltage, 12.5 V, to pull the “OE. the terminal of the 27C1001 high, which allows the device to be programmed. The VPP input of the 27C 1001 is held either at +5 V (during reading operations) or at about +12 V (during programming). To ensure that the 27C1001 is supplied with a sufficiently high operating voltage (nominally 5 V). a Schottky diode type BAT85 is used in position D2. Tills diode is marked by a forward drop of 0.2 V only.

1-Mbit adaptor for EPROM programmer Schematic diagram

Switch S1 takes the highest address input, A 1 6, of the 27C1001 low or high to affect the selection between the lower and higher 64 Kbyte block in the device (A16 = low, and A16 = high, respectively). Diode D5 lights when the lower block is addressed.

The construction of the adaptor is apparent from the PCB layout. Start by fitting the single wire link on the board. Socket 1 is fitted at the track side of the board and consists of two 14-pin PCB pin headers. Switch S1 is a self-locking push-button from my with a built-in LED indicator. The PCB accommodates both 28-way and 40-way ZIF sockets.

1-Mbit adaptor for EPROM programmer Schematic diagram
Parts list
R1 = 10 kΩ
R2 = 1 0 kΩ
R3 = l 00 kΩ
R4 = 1 kΩ
R5 = 100 kΩ
C1, C2 = 100 nF
C3 = 1 nF
DI = zener, 5.6 V, 400 mW
D2 = BAT85
D3 = 1N4148
D4 = zener, 8.2 V, 400 mW
D5 = LED 3 mm
Integrated circuits
S1 = self-locking push-button switch with integral LED
2 off 14-way strips of PCB pins (long pins at one side)

1-Mbit adaptor for EPROM programmer Schematic diagram

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