GoSDC SD Card Interface In-Depth Review

A few weeks ago we broadcast an article covering a number of the hottest SD interface cards on the market today. Today it's time to look specifically at one of them - the GoSDC for the Acorn BBC Micro, Electron, B+, Master and possibly some earlier Acorn computers.


Ordering and Delivery

The GoSDC card is the creation of John Kortink who has a passion for creating Acorn replacement circuitry and enhancements. Before the GoSDC came the GoMMC, which achieved the same goal of providing an MMC-card compatible interface to the Acorn computer. The GoSDC is an evolution of that, providing enhancements such as SD and SDHC card support with capacities larger than 4GB, and a 1MB flash ROM that contains all the filing systems and tools required to use the GoSDC. John's hardware can be viewed and ordered directly from his website and paid for via Paypal. It costs 60 Euro plus shipping. The ordering and payment process was quick and simple. His website provides several choices of GoSDC card and adapters to suit your Acorn retro needs. The 'MBE' version is the standard one which works on BBC Model B running OS 1.20 or higher, BBC Master running MOS 3.20 or 3.50, and Electron. The 'UNI' version supports all the MBE machines but adds support for the B+. It does not rely on being able to do writes to ROM (which is possible on the BBC model B, BBC Master and Electron, but not on the BBC B+), but instead uses some clever trickery to do write operations. This means it has a lower write performance than the MBE version. I went for the 'MBE' model. If you want the GoSDC to work with an Electron one of two special 'GoSDC to Electron' interfaces are available for an extra 15 Euro. One uses the Electron expansion port, and the other uses a Plus 1's cartridge slot. From ordering to shipping took 5 days, and then delivery was a further 6 days from The Netherlands to UK.


The box arrived in one piece with good foam wrap packaging for the main GoSDC unit:


The contents of the box include (from top-left, clockwise): An 'adapter' ROM slot with flying lead (used in BBC model B installations only), GoSDC board in ESD bag, 16 MB MMC card, and a spare ROM slot used in BBC Master installations to give GoSDC more height above surrounding circuitry.


The topside of the GoSDC consists of a CPLD, or Complex Programmable Logic Device, which is an Altera Max3000, an SD slot and some jumper pins. The underside is dominated by the 28-pin plug that will go into the computer's mainboard, a 32 KB SRAM in the middle, and a 1 MB flash ROM and a crystal oscillator:


The Mule

The testbed for the GoSDC is my Acorn BBC Model B with an Issue 4 mainboard. It has no other ROMs or Econet, so it's completely vanilla. It meets the minimum requirement that GoSDC has for the Model B, which is OS 1.20. I have not used a BBC computer since about 1982 when they were introduced into British schools, thought I have owned this particular Model B since around 2006. It's in excellent condition and I even have the original box with the serial number sticker and polystyrene inserts.

My aim is to enhance the usability of this Beeb with a good selection of instantly playable games and adding a Disk Filing System in a single solution, which the GoSDC is able to do. Taking apart the computer is straightforward. Two screws on each side at the rear of the unit, and on the underside, two more screws at the far front. Flipping the computer back over, this allows me to remove the top part of the casing, as seen in picture 3 above. Two more screws on either side of the keyboard allow the keyboard to be pulled slightly away from its normal position (pic 4), revealing the ROM slots in the lower-right of the main board (picture below). Note the OS and BASIC ROMs taking up the two leftmost slots. At this point, we're ready to install the GoSDC.


Installing the GoSDC Hardware

I downloaded the latest version of the GoSDC software, which contains a folder structure called 'Documentation'. This goes into a lot of depth about the capabilities of the GoSDC, with descriptions of the commands available, and how to install and set it up for use. I tried following this, but as a non-BBC-savvy owner, I'll admit to getting slightly lost along the way. From my youth I can recall how to access a disk's catalogue, and how to load programs, but I've never installed a ROM so terms like 'sideways ROM' and 'sideways RAM' meant little to me before I started this process. Fortunately, John was very quick at emailing me back when I posted queries. The hardware installation was actually quick and painless. I installed the GoSDC into ROM slot 13 (IC88), right next to the BASIC and OS ROMs. I then installed the 'adapter ROM' into the far-right ROM slot 15 (IC101).

I then connected the flying lead from the adapter ROM to the GoSDC (see picture 2 above). The online instruction manual states:

Only with the adapter installed, GoSDC can use the 'free ROM bank on GoSDC' to auto-load patched filing systems (refer to other parts of this manual for details). If you have sideways RAM banks in your machine that GoSDC can use instead, or you're going to have one or more PROMs with a particular patched filing system permanently installed in your machine, installing the adapter is not really necessary.

So the purpose of the adapter ROM for Model B installations starts to become clear - it is to allow a disk filing system ROM to materialise to the Model B in that far-right ROM slot, controlled by the GoSDC, or to put it another way, the GoSDC has within it an additional 'free' ROM slot, and it is in this that we load the DFS or ADFS ROM to provide disk capabilities to the Model B.

At this stage, we can put the keyboard back in position, but I would recommend not screwing it in place yet, until we've tested that everything works.

Now the hardware installation is complete, click here to move on to Part 2.


This page was last updated on 5th February 2015.