*** This item now includes the User Port Micro SD storage system ***
This upgrade gives an unexpanded BBC Model B eight banks of 16kB sideways RAM plus a further eight flash ROM images. It therefore allows up to sixteen ROM images to be loaded in the Beeb at any one time, the maximum permitted by the Model B's design. The kit is complete with battery backup and various write-protect options for the 128kB static RAM chip.
The board essentially offers the main features of the previous RAM/ROM board but has been designed to reduce the number of flying leads and generally simplify installation. The small probes often used for attaching wires to the pins of chips can work well enough, but they can also be tricky to fit if space is tight, under the keyboard for example. Here, just a single wire is needed that pushes onto part of link S21 on the motherboard and no clips are required whatsoever.
The RAM/ROM board itself is completely built and tested, indeed the flash ROM is actually pre-programmed with data in a Model B. It fits in one of the four ROM sockets in the front right hand corner of the computer (partially under the keyboard) and also into the main 6502 socket. No track cutting or soldering is needed during installation and the upgrade is easily removed if this were ever required.
One of the Beeb's most useful features is the concept of the sideways ('paged') ROM system. This allows up to 16 different ROMs to be present at any time, but the standard Model B only offers four ROM sockets on the main board. Traditional ROM expansion boards provide an extra 12 ROM sockets and, if you are lucky, a single bank of RAM. EPROMs have the obvious advantage of not losing their contents when power is removed but cannot have their contents readily changed. The reverse is true for sideways RAM.
Sideways RAM with battery backup gives you all the advantages of both EPROM and RAM with the added bonus of write protection to prevent accidental corruption. Most users have some favourite ROMs which they just can't do without and a few that they use occasionally. With eight banks of RAM at your disposal you can just load the ones you need, whenever you want. Got a ROM that clashes with something else? No need to physically remove it, just clear the bank of RAM and simply load it again when needed.
If you have the Turbo MMC system you can load all eight banks of RAM in under five seconds. You can do the same with floppies of course, it's just a bit slower. Anyway, with the battery backup system you won't need to keep loading the data every time the machine is switched on.
All of the 16kB banks of flash memory (up to eight) are programmable in the machine.
How do I program the flash ROM?
The flash ROM is easily and quickly programmed while
it's in the machine. You'll need the supplied software to do this. The program
is on the supplied CD as an SSD image, but for convenience it's also on the
flash chip itself in ROM Filing System format. The CD explains how to copy this
to your usual filing system so there is no need to keep it on the flash ROM
indefinitely.
How long does programming the flash ROM
take?
The actual program/verify process takes about one
second to program 16kB of data in the computer's memory into one of the
available banks of flash ROM. That is far quicker than programming an EPROM and
indeed only marginally slower than loading data into ordinary sideways RAM. An
EPROM also needs 25 minutes or so of UV exposure to erase it whereas the flash
chip
can be reprogrammed at any time with no lengthy erasure process needed.
Current requirements
The Beeb's power supply cannot supply infinite current and the more you draw
from it, the hotter it tends to run. This upgrade draws a fraction of the
current needed by typical ROM boards from the 1980s. Being physically far
smaller, it doesn't interfere with air circulation in the same way that the
original 1980s boards did.
Do I need to write protect the flash ROM?
Generally there is no need although it is possible to do this. Before writing of data to the device
can take place, certain bytes have to be written to certain addresses and in a
particular order. Failure to observe this protocol exactly means that the data
write operation will fail. The flash ROM is as
immune to corruption from spurious writes (during power on/off for example) as
it's possible to be.
The chances of software randomly writing to the chip and stumbling upon the precise, correct sequence needed to alter it are one in many millions. It just isn't going to happen.
What are the main differences between flash
ROM, EPROM & sideways RAM?
EPROM: Ideal for ROM images that are important, reasonably stable
(bug-free) and required at all times (eg main filing system, BASIC). Normally
EPROMs are completely safe from data corruption issues and cannot be
accidentally overwritten. The disadvantage is that a
separate EPROM programmer is usually required and perhaps a UV erasure unit if
you need to make changes later on. They cannot be programmed or erased in the machine.
Sideways RAM (implemented with static RAM): Very low power and ideal for temporary ROM images that are needed occasionally. Images may be loaded very quickly from a storage system (floppies, MMC, Compact Flash etc). The supplied battery will maintain the data for years when the machine is off. Sideways RAM is also ideal for applications that use part of the sideways ROM area for workspace such as an E00 filing system or printer buffer.
Flash ROM: Like EPROM, this is well suited to ROM images that are essential and do not need to be changed very often. No battery is required for data retention and its inbuilt protection system against spurious writes during power on or off is virtually 100%. Its key advantage over EPROM is that it can easily and quickly be reprogrammed in the machine. The way the flash chip works is such that data bytes must always be written to a blank location (ie containing &FF). That's not a problem when reprogramming an entire 16kB ROM image, but it's no good for situations where just a few bytes need to be altered with immediate effect. That's where sideways RAM should be used.
How do I get ROM images into sideways RAM
or flash ROM?
There are basically two ways. One is to download the required ROM image from the
internet to a standard PC. You will then need to bridge the gap between your PC
and the Beeb, something that is usually very easy to do if you have one of the
modern solid state storage systems.
The other method is to insert the actual ROM (assuming you have it, obviously) into one of the two rightmost sockets on the motherboard. A link on the RAM/ROM board is then changed and this has the effect of activating those sockets. You can then save a copy of those two sockets to disk and software is provided to do this. This process will need to be repeated for each ROM that you wish to use later on.
Finally, once the ROM images are available on disk, they can be loaded into sideways RAM (or programmed into the flash ROM) as and when needed using the supplied software.
How long will the backup battery last?
With the battery backup in place the contents of all eight banks of sideways RAM
will be retained even when the computer is turned off. The current drawn from
the battery in standby mode is under one microamp. The lithium coin cell provided should last for
around four years,
although you might get away with longer.
Can it be used with an existing ROM
expansion board?
No. There would either be an electronic incompatibility or the two boards just
wouldn't physically fit at the same time, or both. Any existing ROM board would
need to be removed first.
Can it be used with a cassette tape
machine?
Correct operation of the upgrade is not dependent on the filing system being
used. However, to get the best out of this type of product you need
a readily available library of ROM images. Some filing systems are too
restrictive and slow and a machine fitted only with a cassette tape for loading
and saving data is not really suitable. Ordinary floppy disks are fine (DFS and
ADFS) and better still, of course, is one of the modern solid state
storage systems (Micro SD, Compact Flash, Gotek etc).
Preloaded ROM images
The board is tested and programmed with data in a Model B computer. This is part
of a routine testing procedure but it also means that you have various ROM
images to experiment with as soon as it's installed. There's a game of Snapper,
Rocket Raid, Chuckie Egg, Space Invaders and Meteors. Of course, they're not
physical ROMs, just data written into the flash ROM (or static RAM) chip. You
can save these ROM images to any suitable storage system (floppy disk, MMC etc)
or overwrite them at any time in just a few seconds. You don't have to keep them
loaded on the upgrade board permanently.
Free PSU capacitor servicing
kit
The Beeb's power supply (PSU) is well known for having capacitors which, after
30 years or so, are prone to cracking open with a cloud of acrid smoke. The free
capacitor repair kit is exactly what it says. Although a capacitor kit for the
Beeb is available as a separate listing, a significant proportion of the cost is
actually the postage and packing. So if you need a capacitor kit for the power
supply then just ask for it at the checkout and it will be included free of
charge. (Although this RAM/ROM board is only for the Model B computer, the PSU
servicing kit is also suitable for the B+ and Master 128)
Money-back guarantee
The product is covered by a 1 year guarantee. Additionally, most eBay Buy It Now sales are covered by the Consumer Contract Regulations (CCR). In essence this gives you a 30-day period in which to return the goods for any reason whatsoever. If you wish to return this item in the 30-day period then you will receive a full refund (cost of the item itself and the postage too). The cost of returning the item to us is to be borne by the purchaser unless, of course, the item is actually faulty in which case we will refund any reasonable postage costs as well.
For UK buyers this offer is extended further. You can return the item in good condition for any reason whatsoever within 30 days for a full no-quibble refund. Not only do we refund the full amount paid but also the return postage (first or second class standard). What do you have to lose by checking it out?