ATMEL AT29C256 32k Flash Programmer

This is a simple circuit I designed to dump/program the ATMEL AT29C256 flash using a standard bi-directional parallel port. The ATMEL flash devices can be ordered from Pioneer Standard for around $5 each.


Schematic capture and layout were accomplished using EAGLE Light from CadSoft. Considering that it is free (as in beer), it is a decent tool. If you see areas for improvement in this design, please don't hesitate to let me know!


#AHEN (U1:9)Address HIGH Register Enable (select)
#ALEN (U1:12)Address LOW Register Enable (select)
#FLEN (U1:11)Flash Enable (select)
DATA[0:7]8-bit Data Bus
ADDR[0:14]15-bit Flash Address
/LINEFEEDDevice Address (select) low bit
/INITIALIZEDevice Address (select) high bit
/SELECTRead/Write (Low = Read)
/STROBELoad Data (on low going pulse)

Theory of Operation

The 15-bit flash address is written into the two 8-bit registers, one byte at a time. 8-bits of data is then written to (or read from) the flash device. The "initialize" and "auto-linefeed" signals are used as a 2-bit "device address" to select which device will be written to (address high register, address low register, or flash device). Note that the flash data is read/write, whereas the address registers are write-only.

Reading/Writing the Registers and the Flash

To perform a write operation to a device, first the device address is set, then the data is presented on DATA[0:7] and a low-going pulse is sent on the STROBE line. Note: Remember that some signals in the parallel port control/status registers are inverted by the hardware!!!


Currently, the programmer is prototyped on a couple of breadboards from Radio Shack. I'm looking into having a PCB fabricated.

Bill of Materials

Ref.Qty.Part #Description
X21N/AStandard DB25 Male Connector
U1174HCT1392-line to 4-line Decoder
U2174HCT02NQuadruple 2-input Positive NOR Gates
U3,U4274HCT273Octal D-Type Flip-Flop with Clear
U$21N/ALED for indicating "power on" (optional)
R11N/A1k-ohm 1/4-watt resistor for "power on" LED (optional)
N/A1N/A28-pin ZIF socket for flash (optional)
N/A2276-174Archer Experimenter Socket (Radio Shack standard breadboard) (optional)
N/A1273-1695Radio Shack Digital Camera Power Supply (3-6.5V, 2.5A)
N/A1N/ARadio Shack 2-wire breadboard adapter for power supply


I need to clean up the source code before I post it. Contact me if you would like me to send you a copy via e-mail.

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Updated 2002.07.14 / T.K.M. / tmcintos(at)
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