*** UPDATE March 2014 :
the original files of this project has been lost , deads together with the pc where they were saved (remember that this is an old project dated 2008). The good news is that I'm planning to revisit the entire project, perhaps with a flash rom pin-to-pin compatible with the old eprom ***
As you can see, the hardware is very simple:
- an Atmel microcontroller that send/recive the data with PC via rs232 serial connection (the MAX233 ic can be replaced with a more cheap MAX232 or other 232 driver)
- one fixed voltage regulator (+5V) as power supply for ICs , two non-fixed voltage regs which provide a 6,5V and 12,5V for programming operations of the eproms
- a four microswitchs for routing the programming voltages to the eprom pins
As you can see from schematic, the eprom used is a 27C256 model, but others eproms are supported:
- 2732 (4 KBytes) : connect address line from A0 to A11, leave A12,A13,A14,A15 unconnected
- 2764 (8 KBytes) : connect address lines from A0 to A12, leave A13,A14,A15 unconnected
- 27C128 (16 KBytes) : connect address lines from A0 to A13, leave A14,A15 unconnected
- 27C256 (32 KBytes) : connect address lines from A0 to A14, leave A15 unconnected
- 27C512 (16 KBytes) : connect all address lines from A0 to A15
In order to keep the project cheap and esay to build, I've used a microswitch instead of dedicated ICs for switching the different voltages routes , so a few words about microswitchs are needed; during read operations , the eprom needs only +5v on both VCC and VPP pins : this is possible to keep close (ON position) the micros #1 and #3 and open #2 and #4 ; due the presence of diodes the real voltage will be around 4,75v - 4,80v , but these values are in the specs of eproms. During programming operations , first close (ON) the micro #2 and than close the #4 : in this way you can give first the 6,5v to VCC pin and than the 12,5v to VVP pin ,in according to the various eproms's datasheets concerning the voltages transition. If you want to return in read mode first open the micros #4 and than open the #2.
Also the PC software is very easy and intuitive
Hereby the commad buttons and options explanation :
- "EXIT" button. Doesn't need more words...
- "Open COM" : set and open the comunication between PC and programmer over serial port.
- "Eprom Model" : you can choose the eprom model to burn.
- "Start Address" : here you can write the address at which the programmer starts to write or read the data to/from eprom (decimal and hexadecimal value are allowed)
- "Bankswitch" : same of above; instead to write manually a start address, you can choose a series of predefined value
- "Nr. of Bytes" : this value is the number of bytes that should be wrote/read into eprom by programmer. This field is automaticly filled when you choose to load a "bin" file (see below)
- "Read Start" : pressing this button, you can read the content of eprom at start address previously set , for a specified number of bytes.
- "Save Bin" : save the content of read eprom in a file.
- "Write Start" : write data to eprom at specified start address; the number of bytes written are equal to the number of bytes previously inserted. Before to start to write, you must load the data (see below).
- "Load Bin" : you can load data (bin file) pressing this button; a windows is opened with the data; the field "Nr. of Bytes" is filled with the number of bytes contained in the bin file.
- the possibility to programming only a specified portion of the eprom , at specified address for a specified number of bytes. This means that doesn't need to erase whole eprom if you want to write a blank range.
- the possibility to "see" the eprom > 4K as a virtual "more than one" 4Kbytes eproms with the "bankswitch" method
- load the first bin file of the your first application/demo/game by clicking on "LOAD BIN" button; choose the file and than OK. A new window appears with the content of the selected file
- now click on "Bankswitch" and select the value 0x0000 is you want to program the file in the first 4K bank
- operate on the microswitchs to put all to ON as describe above
- than click on "WRITE START" button in order to start the programming operations; a progress bar shows the precentage of the process.
OK now ,using the same steps , you can select your second application/demo/games that you want to save on eprom, select a different bank at value 0x1000 and start the write operation; and so on...
then, you ca use this eprom in your Atari 2600; for select the game you must tied to 0 volt or tied to +5 volt the A12, A13 and A14 eprom's pins as describe in this table:
As power supply, you can use a laptop PSU that usually has a 18 Vdc output.
If you want the firmware for the MCU and the software for PC program, simply email me and I will send both files. If you are not able to program the Atmel MCU, send me a blank MCU : I' ll flashed for you and I' ll send back