Hywel Francis tackles an EPROM programmer for the Dragon 32

With Dragon computers spread almost world-wide, there still seems to be a large market for add-ons. This EPROM programmer should be a welcome addition for the MC6809E enthusiast and beginner alike. It allows Dragon owners to 'burn' their own firmware into EPROM, making the machine a cost-effective industrail control tool, giving more protection to those in the machine code game, or just making home-grown software more convenient.

The unit plugs into the Dragon 32's cartridge port and, since it needs no external power supply and its Operating System is on ROM, it will auto-boot as soon as the Dragon is switched on.

Initially, you are presented with a menu of 12 EPROM device numbers. After a selection has been made, another menu comes up, with the 12 available functions. These allow complete control over the loading, checking, and addressing of the EPROM.

Programming the EPROMs is simply a matter of selecting the device to be programmed, and downloading the data held in memory. The data is then burnt into the EPROM at the speed required by the manufacturer's specification. For some devices, this can take quite a while although the new Intel algorithm shortens this time considerably for some devices. So, what do you do when you have programmed your EPROM? Well, there are three options.

You can open up one of your old Dragon Data cartridges, remove the EPROMs, and replace them with your own. The drawback here is that these cartridges will only accept two 4K 2532 EPROMs but, with a slight modification, two 4K 2732s may be used.

Alternatively, you can use the sideways intelligent ROM board, available from the same supplier, which will hold up to three ROMs. Each of these may be invoked by on-board software.

As for the final possibility - if you are handy with a soldering iron, obtain a printed circuit-board that can be plugged straight into the Dragon's cartridge port. This has all the correct pin-outs, and is also available from the same supplier.

The comprehensive manual supplied with the unit assumes no prior knowledge of EPROM programming and states boldly: "The need to refer to this manual will be a rare event after the first perusal." In fact, the only time I needed the manual was to check the various EPROM sizes.

Although there are a number of EPROM programmers on the market, this particular unit offers several advantages over its rivals. No external power supply is needed for the programming voltages and no complicated DIP switches are used to select the appropriate EPROM - this is done in the software. There is automatic overload protection if the EPROM is inserted the wrong way round and the menu-drive software is quite comprehensive. The programmer is probably a worthwhile investment whether the EPROM to be copied holds Z80, 6502 or even 68008 software.

A recent innovation announced by Intel dramatically reduces the programming time for the 2764 (8K) and larger EPROMs. Previously, the manufacturer specified that each location in the EPROM could only be programmed by applying suitable logic pulses of 50 milliseconds duration to each location. This meant that programming a 2716 with 2048 location would take 2048 x 50 = 102.4 seconds.

To program a 2764, 8192 locations would take four times as long - nearly seven minutes. On this sliding scale, the large 27256 (32K) could take nearly half an hour to program.

Intel's Innovation works by applying short, 1 millisecond programming pulses to the EPROM, and continually monitors whether the data has been successfully burnt in at that location. Because of this factor, only a minimum amount of time is spent at each location in order to make sure the correct data has been programmed into the chip.

The programming times achieved by this method are considerably less than before - an 8K in 50 seconds and a 16K in 100 seconds. This compares favourably with the 2716 (2K), where this technique cannot be used.