The EPROMS I got were from the well known auction site (not sure if I can post the link to them).

I've only just seen the replies to my predicament I'm experiencing. But this takes a longer overall time to program an entire EPROM. Older programmers instead applied the programme data for the total length of the delay as per the EPROM manufacturers data sheets. Then a final burst is applied to try to ensure that the data stored will be reliable. This repeats until either a time out occurs or the EPROM correctly retains the data. Modern programmers use burst mode, which means they keep trying with short bursts, read the data, compare to the value that should be stored, if there is a difference go back to burst mode to try again. The delay time is provided, because different EPROMs may need the data to be held for a different amount of time while each byte is programmed. If there is a problem with the DC-DC inverter, none of the EPROM cells will be programmed properly, or maybe just the first handful will be and then the rest will fail to be programmed properly. That way, it may be possible to work out if all bits are affected or just one or some are affected.ДЄnd yes, programmers use a DC-DC inverter to get the high programming voltage (be it 12V, 12.5V, 13V, 13.5V, 21V or 25V). So try a test file made up of 0XFE, 0xFD, 0xFB, 0xF7, 0ењЋF, 0xDF, 0xBF, 0x7F, 0x00 ensuring that you use a вЂblankвЂ™ EPROM. When a memory cell is programmed successfully, the analogue comparator circuitry will see a different voltage level, which is read by the CPU as a logic 0. An empty ROM should read as 0xFF (that is all data bits return binary вЂ1вЂ™). You are better off using a short test file when trying to вЂburnвЂ™ an EPROM on a suspect device. Is there some king of inverter in the box? I qoukd of course need to erase them first using a UV box.ДЄlso how does it get 12V or 21V from the User Port. So my idea is to build the programmer from the beebug magazine and see if I can use those that I already have. They are ones I got with a whole bunch of other stuff when I bought a job lot of BBC stuff.

These are the ones with the square window in. I do still have some old eproms that have been stored in my mums loft for ages. IвЂ™m sure he would prefer to consider these things before he starts buying parts. If Brett is building his own EPROM programmer and wants to use larger capacity EPROMs, then we can discuss the options. If he decides he does want to build an EPROM programmer, and he asks for help of course, help will be offered. Some types of EEPROMs can be programmed in a Beeb with a minor wiring change.Д«rett now has the option of how he wishes to proceed. Sat 6:39 Chris - True, but if you were not aware of the existence of EEPROMs, you may think that the only type of non-volatile memory chip you can use in the sideways ROM sockets of a Beeb is EPROMs. I will have a read of that thread you linked to. I do recommend having a look at using EEPROMs before considering EPROMs There is a (bedtime reading) thread about using EEPROMs here. Some types of EEPROM chips or flash RAM chips can also be used. Then the machine will see them as four 16K byte вЂROM chipsвЂ™. You can wire up in an extra wire, then the machine will see one physical chip as two 16K byte вЂROM chipsвЂ™.Дў7512 or 27C512 are double the capacity of a 27256 / 27C256. But only half (16K bytes) can be normally be seen by the microprocessor. The smallest currently available (from the main electronic suppliers) EPROM is a one time programmable (you can вЂburnвЂ™ them, but there is no window to erase them) 256K bit (32K bytes) EPROM such as a 27C256.

You may be able to find some on internet trading sites, or from suppliers that still have old stock. Or you can also use a 128K bit (16K bytes) EPROM such as a 27128 or 27C128. But these have been obsolete for many years. For the BBC B, the standard ROM is either a 64K bit (8K bytes) EPROM such as a 2764.

Diy eprom programmer