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Eprom Programmer Mark 2

Eprom Programmer Mark 2

The programmer itself is dumb and is controlled by the host computer via the RS232 serial port (COM1 or COM2). Device selection and operation mode is set by front panel switches.
How it Works
The circuit diagram is spread over a number of illustrations. Although it may initially look complex, it is in fact relatively straightforward. When a “-” follows a signal name (for example STROBE-), this shows that the line is active low. When a number is followed by an “h” this indicates that the number is hexadecimal.

The pinouts of the four EPROM types handled by this unit are shown in the table below.

PIN 2764 27128 27256 27512 
1 VPP VPP VPP VPP 
2 A12 A12 A12 A12 
3 A7 A7 A7 A7 
4 A6 A6 A6 A6 
5 A5 A5 A5 A5 
6 A4 A4 A4 A4 
7 A3 A3 A3 A3 
8 A2 A2 A2 A2 
9 A1 A1 A1 A1 
10 A0 A0 A0 A0 
11 D0 D0 D0 D0 
12 D1 D1 D1 D1 
13 D2 D2 D2 D2 
14 GND GND GND GND 
15 D3 D3 D3 D3 
16 D4 D4 D4 D4 
17 D5 D5 D5 D5 
18 D6 D6 D6 D6 
19 D7 D7 D7 D7 
20 CE CE CE/PP CE/PP 
21 A10 A10 A10 A10 
22 OE OE OE OE/VPP 
23 A11 A11 A11 A11 
24 A9 A9 A9 A9 
25 A8 A8 A8 A8 
26 NC A13 A13 A13 
27 PP PP A14 A14 
28 VCC VCC VCC VCC 

NC = No Connection
PP = Program Pulse, Negative Going
OE = Output Enable (Active Low)
CE = Chip Enable (Active Low)
VPP = Programming Voltage
VCC = Supply Voltage
GND = Ground (0V)

Construction
The unit is assembled on a single sided PCB. A number of wire links are required, which should be fitted before any components, since some pass underneath ICs. I would suggest that the resistors are fitted next, followed by the ICs, then the capacitors, then the remaining parts. Fit a link wire between COM and 96 to set the Baud rate to 9600. Fit SIL header strip or Veropins for the off-board connections.

Fit a 28-way IC socket in the EPROM socket position. Plug three more sockets into this, then plug the ZIF (Zero Insertion Force) socket into the top. If this stack feels unsteady use some Araldite or similar to hold it together. The interwiring is shown in figure *. This should be carried out at this stage, since it is necessary for testing. After testing the board can be fitted into the case.

The connections for both 9 and 25 way serial connectors, use whatever matches the socket on your computer. On the prototype a 9 way D connector (serial) and a 6 way DIN socket (DC input) were fitted to the case.

Testing
Connect the unit to a 5V and 12.6V supply. If a test meter is to hand, check for about +9V on pin 2 and -9V on pin 6 of IC1 (MAX232).

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