Current events

More prototyping tools: XC9572 breakout board

XC9572-XL in a TQFP-100, mounted to the breakout board

Christmas Eve afternoon was spent making the breakout board shown in the photo, and I had enough time before Christmas dinner to check that the board at least programmed correctly (which it did), so I don't think I screwed anything up too badly :-) This is the chip I intend to use as the CPLD on the ethernet board. It has more pins than I actually need, but the next size down is the (more expensive!) PLCC, and then to the 44 pin packages which don't have enough pins.

Apart from pin headers/SIL strips, everything is surface mount, using the passives I intend to use for the final board. The 3.3v power circuit (using a 3.3v low dropout regulator, no heatsink required since the current draw won't be that high) is also the one I intend to use on the final board. Decoupling capacitors are all 0603 sized which is as small as easily hand solderable. I want to get the passives down as small as possible so they don't get in the way too much when routing traces; 1206 is just a bit too big (and gave me a real headache when laying out the W5100 breakout board).

I probably won't get much more done on the project over the next week or two (too many Christmas/New Year type events going on) but hopefully by the end of the month I'll have the W5100, CPLD and memory all working on breadboard and will have sent the first packet.

Winston 10:28, 25 December 2007 (UTC)

Welcome to the wiki

In order to make it easy to document ongoing hardware projects for the Sinclair Spectrum, I've put this wiki into service. At the moment, it can only be edited by me... but in future, I hope there will be others interested in collaborating on the projects here, and MediaWiki makes it easy for others to edit, too.

Onto the most recent news. I've just received my order from Farnell for most of the parts needed to make the prototype ethernet boards. I intend to make a small number (about 8 or so) to allow me to develop ways to economically build boards (economic not just in money, but in time). Experience of hand-making a couple of diagnostics boards showed that this was a non-starter (it took FAR too long - a couple of hours per board at least to assemble!) so this time around, I've decided to use surface mount parts, and build my own reflow system (with a hotplate or a toaster oven - nothing expensive) to try and make the boards reasonably quick to assemble. I also intend to make a handful of prototypes, so I can get a few out to some Spectrum enthusiasts who want to be on the bleeding edge (!) and shake out any bugs.

But in this consignment, I have:

• 10 Xilinx XC9572 CPLDs, in 100 pin TQFP packages. 3.3 volt types (which have 5v tolerant I/O)
• 10 Am29F010 90ns 128kbyte flash memories. This is to hold the ROM code, and a set of applications to go with the board. These are in TSSOP packages.
• 10 IDT71024 128kbyte static memories. Extra workspace for networked applications. These are in SOJ (small outline, J-lead) packages.
• 3.3v linear regulator - to power the W5100 and the XC9572.
• Various surface mount passives (lots of capacitors, a few resistors, a few inductors).
• A couple of tools to make it a bit easier to do surface mount stuff (tweezers, nothing fancy)
• On back-order - 10 Tyco Mag45 RJ-45 sockets with integrated magnetics.

I already have plenty of some of the other parts - lots of 25MHz crystals, enough P and N channel discrete MOSFETs (for the ROMCS hold circuit), indicator LEDs etc.

I still need to get some card edge connectors, LaesQ suggested a suitable supplier (where he gets the connectors for the DivIDE).

The current plan of attack is to make a breakout board for one of the XC9572s, including a 3.3v regulation circuit, and breadboard a test circuit which will include a (DIP packaged) Am29F010, as well as a 1mbit static RAM, and the W5100 breakout board I built earlier. This will enable me to test that the Spectrum's bus doesn't get loaded too heavily (I've already noted that the W5100 puts some loading on the bus from earlier tests), and that the current draw isn't too high; the W5100 can use up to 180mA with the PHY at full power. Once any hardware issues are sorted out, then design the schematics/PCB for the first version of the board... then have PCB Train make 10 of them.

Winston 22:51, 21 December 2007 (UTC)