Paul Hunter of 1630 Forest Hills Dr., Okemos, Mi, 48864, with whom I’ve had the pleasure to converse, is a very congenial chap (English accent and all). He has designed an unique add-on board (written up in various magazines), in particular, the Nonvolatile RAM Board, Based on the 2K 6116-P3 chip (low power CMOS) and a lithium battery, this becomes an excellent system for program development.
One problem haunting both pro and fledgling ZXers alike, is the inevitable crash. With a little forethought and a Hunter Board, this could be a much less terrifying experience. The board comes equipped with a CPU reset switch and jumpers galore to allow flexibility in memory location, power supply and type of memory chip used. The CPU switch resets the CPU to USR 0000 or a cold boot. The Sinclair however, does not use all available ram. On a restart you lose only 16-32K. If you have more than 16K memory, then the extra memory is spared from the crash (not withstanding a runaway LDIR, [or other strange code! – ed.]). If you take the time to make a copy of your program in high memory and with a download routine on the Hunter board, then a reload is as easy as a RAND USR…. A good example of this is HOT Z and its download routine.
Jumpers! You want jumpers! Well here they are. Jumpers on this board allow for either battery power, power from the ZX/TS or an external 5V supply. They also allow the board to occupy any 8K memory block up to 32K. You need not have a full board. You may pop out a chip or two to allow coresidence of an EPROM (on another board) for a special operating system. There are also jumpers to configure the board for NMOS ram or 2716/2732 EPROM as well as CMOS 6116. They may also be mixed! With a little doing, the board can house different types of chips simultaneously. I don’t think too many of us want to make the changes involved (apparently Paul doesn’t either), and I advise getting the second board (unadvertised special), for $20.00 with everything necessary for EPROM.
Paul gives several routines in his documentation for you to put in your new found ram. There is still plenty more left open for other things though. One other convenience he has included is a write protect switch (consists of an additional resistor), Once you enter that MC stuff, you can’t easily wipe it out. Paul notes that occasionally an unpopulated (with CMOS chips) board may have display problems (an apparent capacitance mismatch), As luck would have it, mine acquired this syndrome as well. The fully populated board was alright. A quick call to Paul brought a replacement chip, 74HC139, an high speed CMOS decode chip (substitute for the LS version), These boards are the absolute highest quality that money can buy. When I first opened that mail pouch I was sure I got my moneys worth. I am really looking forward to Paul’s next great achievement,