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E2PROM ProgrammeriRobot Home |
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E2PROM ProgrammeriRobot Home |
E2PROM Programmer Functional DescriptionTo view the schematic of the programmer, click here (10K GIF image). I recommend opening it in another window or printing it out so you can follow along. The QBasic Program to control the programmer from a PC is here (7K BAS file). I do not use standard American component designation conventions in this schematic but instead refer to each device by its generic part number. 7805 RegulatorA 7805 regulates input power of at least 6 VDC to 5.1 VDC. I have not as yet ascertained the minimum current required but would estimate about 500 milliamperes. The filter capacitors on pins 1 and 3 of the 7805 I chose arbitrarily and you may substitute. On the left of the schematic you will find an LED and 270 ohm resistor the purpose of which is to indicate the power is present and the 7805 regulator is operating. Parallel Port InterfaceThe programmer is connected to a computer's parallel printer port like that used by a PC. The connection is generic enough to facilitate use with just about any computer. The connection is depicted on the lower-left of the schematic. The programmer can be written to like printer but the feedback signals a printer usually has are not present. This lack of feedback signals was intentional as it would increase component count and make things more complicated than they need to be. The programmer can also be read if the computer utilizes a bi-directional port. The computer is protected from the programmer by a set of resistors immediately following the port connector. The value of these resistors can range from 1 kilo-ohm to 2.2 kilo-ohm (whatever you have on-hand). At one kilo-ohm, the maximum current that could pass between the computer and programmer is about 25 milliamperes. 74LS175 - SelectionThe 74LS175 facillitates latching in the Intel 8243 to which we want to write and selecting the PROG mode of the 8243. Only three of the four flip-flops are used. The fourth has its D input tied to a logic "1". An RC network consisting of a 1 microfarad capacitor and 10 kilo-ohm resistor provide a momentary clear signal to the 74LS175 at power-up. This is called power-up reset or POR. POR gives us a know state to start from. Since POR clears the 74LS175, the Q-NOT outputs are used to control the 8243s. Thus, the programmer is initialized with both 8243s unselected and their PROG inputs held to a logic "1". 8243 - IO ExpanderTwo Intel 8243s are employed and are differentiated as 8243 #1 and #2. 8243 #1 is dedicated to addressing and 8243 #2 reads and writes data and control bits. An 8243 is comprised of four, 4-bit I-O ports.
Allocation of 8243 Port Resources Programming the 8243
Each of the ports can be designated as input or output. Additionally, as output ports, written data can be ANDed or ORed with the existing data. Take a look at the QBasic program to see how I drive the 8243s. EEPROM Socket
Dip-Switches
SummaryWell, that's it in a nutshell. I'll add more as I get the time. There's enough information on this page to make the device and use it. If you have any problem or need advice or have comments, please, drop me a line. |
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On power-up,
the 8243 is ready to accept an address. A nice feature in the 8243 is that the PROG pin is
sensitive to a state change but not to a one or zero input. That is, if
the 8243 is powered up with the PROG pin at a one state, an address is latched
when the PROG pin changed states from one to zero. The 8243 is then
ready for data. The data is latched when the PROG pin changes states to a one
again. The same function can be obtained by powering the 8243 with the PROG pin at a zero.
The address would then be latched by a zero to one transition and then
data by a one to zero transition.
