Stuart

Well I've gone as far as I'm going with this I think. Website updated with hopefully all the information one would need (www.avjd51.dsl.pipex.com/tms9995_breadboard/tms9995_breadboard.htm) plus EPROM images for BASIC and Forth. To keep Marc happy I've included some details about interfacing a VDP, SID and keyboard, but it will be up to the reader to work out (and experiment with) the exact circuitry required; that's the best way to learn Stuart.

OK, I've got a website half put together - <www.avjd51.dsl.pipex.com/tms9995_breadboard/tms9995_breadboard.htm>. There is a link to the schematic in the Technical Description section, and a link to the EPROM binary image in the EPROM Images section. I'll carry on fleshing out the details over the next week or two. Mark W - if you haven't got the mean to program the EPROM, send me a PM. Stuart.

Worked out how to post a picture ... Stuart.

The wall plug one from Ebay? It hasn't arrived yet, but I've got a matching socket from Maplins that I'll probably just glue to the side of the breadboard, and run a pair of jumper wires from that. S.

Happy to report that I've got my breadboard system running the system monitor from TI's 9995 evaluation module. I had the CRU base address for the 9902 wrong - I thought it was >0080, but its actually >0000. So I need to correct the circuit schematic. It's also happy just using the Tx, Rx and Gnd lines on the serial port, so I can delete some wires from that as well. I'll try to make a start getting the details on a website this week, along with a binary dump for the system monitor for programming an EPROM. Stuart.

Loads of them on Ebay. The 74HCT259 matches the TTL LS logic levels ... but I'm now sure how it would get on directly driving an LED. Might be better, might not be able to cope. I'm sure someone else could advise. Stuart.

Hi Mark, My breadboard arrived yesterday and I spent a rather long evening wiring it up. I know the processor is 'clocking' but no luck getting anything on the serial port yet. May be a simple wiring error, or something more fundamental - I need to write a few simple test routines so I can probe around the circuit and see what's going on. I'll try to attach a photo of my efforts so far. I want to install a ZIF socket for the EPROM so I can change it easily. Wiring on the breadboad - I used Maplins solid core wire - order code BL85G. They've got different colours (with different order codes) - get several and use the different colours for the power supplies, address bus, data bus and control signals. Get a pair of wire strippers. Crystal - I got one off Ebay that seems to work: Ebay item # 260873095032. Power supply - if you don't really want to buy a full blown bench power supply, I've got a regulated +5V plug supply on order which I think will do the job - Ebay item # 250910940846. I'm currently using a spare TI-99/4A supply ... with its horribly bulky transformer. Software controlled LED - a 74LS259 is perhaps a bit more flexible than a 74LS75 (it gives you 8 outputs). Needs some decoding circuitry as well. The '259 will drive an LED directly - needs a ~330 Ohm series resistor. Connect the LED to +5V, and use a logic 0 output on the chip to light the LED. I'll keep you posted. Stuart.

For the DX10 stuff, first check to see if its already on <http://www.bitsavers.org/pdf/ti/990/>. That might save you hours of scanning time ... Stuart.

All the MAX chip (in the schematic) does is convert TTL<>RS-232 voltage levels. The UART is actually the 9902. The 16550 UART, as used in the PC for donkey's years, includes a FIFO and interrupts, and might be "interfaceable"? Stuart.

I've put the schematics and PCB layouts for my three TM990 cards on my website if you want to take a peek. Go to <http://www.avjd51.dsl.pipex.com/tm990/tm990.htm#modules_and_docs>, then scroll down and you'll see my three cards at the bottom of that section. There are links to the schematics and layouts (as PDFs) on the right. You'll probably recognise the part of the schematic for the SID interface. Still waiting for the breadboard and EPROMs to be delivered for the 9995 project. You could use a UART for the keyboard interface if you can find an old keyboard that outputs RS-232 serial. Some old keyboards output ASCII over a parallel interface and you could connect that up using a 9901 - done that with a TI-99/4A years ago. Setting up a 9918 on a breadboard has also been done before - take a look at < >. Stuart.

Hi Mark, ROM and RAM chip selects. As Jens-Eike says, /RAM_CE is not simply the inverse of /ROM_CE. Both /CE's have to be gated by /MEMEN so that memory is only enabled during a memory cycle. Schematic software - I use the software from (and get PCBs manufactured by) www.expresspcb.com. Advantages: its the company that Jon Guidry used to produce the bank-switched cartridges, and he was happy with their service, so I was happy to trust them for my first PCBs. No practical limits on number of components or PCB size. Disadvantages: it saves/outputs in a proprietary format so you can only get PCBs designed with their software manufactured by them (fair enough). No autorouting on PCB layout (but hey, doing the layout is fun!). Their shipping to the UK is a significant cost, as they only provide a sort of 'next-day' service. ---- Free non-proprietary software is available but all the ones's I've seen are limited to a PCB size of only a few inches square, which is no good to me. So you'd have to pay for software, then find a UK PCB manufacturer you can trust, and for small quantities it's going to cost around on par with using expresspcb.com. Clock speed - 12 MHz crystal is divided internally by 4 to give a 3 MHz clock, as Jens-Eike says. READY is pulled permanently high so the automatic wait state generation is invoked, which I will need for the 300ns EPROMs I have ordered, and it also simplifies the design as disabling wait state generation would need another IC, and I want to keep the number of components to a bare minimum. You could add the extra IC later if you had fast memory and no wait states. Don't go buying bits too early folks until its working. Especially not the 9995s for $120 a pop ... Stuart.

I've drawn up a schematic and parts are on order to test it with. TMS 9995 Breadboard Project Schematic.pdf The design gives 32K EPROM and 32K RAM. Although the system monitor code is only 6K, having a large EPROM simplifies the design and should enable use of a modified 24K Powertran Cortex Basic and figForth (and perhaps Mark Will's TurboForth as well if it can be 'unpackaged' from its bank-switched design). There will no ability to load/save programs. Input/output is over an RS-232 interface to a PC running a terminal emulator such as the free TeraTerm. I'm hoping it can be assembled on breadboard so no soldering skills will be required (although it might be necessary to solder a few wires to the RS-232 connector). Stuart.

Well it did actually get me thinking about exactly what you would need for a minimum system, and whether it could be reasonably assembled on a small breadboard with jumper wires. Currently thinking along the lines of: -- TMS9995 processor, which includes 256 bytes of RAM on-board -- 12 MHz crystal -- 74LS138 memory address decoder -- EPROM programmed with system monitor -- 74LS138 CRU address decoder -- TMS9902 RS-232 interface -- 75188(?) RS-232-to-TTL level converter -- 75189(?) RS-232-to-TTL level converter -- 25/9-way D-type connector for RS-232 -- some pull-up resistors -- decoupling caps -- reset switch -- +5V voltage regulator so you can run it off an unregulated supply (optional) -- would also need a -5V supply for the RS-232 - although I think there might be an RS-232 level converter that includes an inverter Although suitable system monitor code already exists, the problem for most beginners would probably be programming the EPROM. Although I'm sure some helpful people would be willing to assist for the price of a few beer tokens. Stuart.

The schematics for the 9995-based Powertran Cortex are on the website that Jean Louis pointed to above - look on the Documentation menu then scroll down to the "ETI Construction Articles and Additional Hardware" section. It's quite a complicated machine but you could pick some of the bare essentials out of it. I've also got some details of a very basic 9995 evaluation module here <http://www.avjd51.ds...eval_module.htm>. No schematic, but there is a partially disassembled system monitor program that might be useful. Datasheets for the 9995 and its various support devices are freely available on the web. Stuart.

For the record, I read that anything with an access time of less than 490ns should be OK for a 3 MHz 9900 with no wait states. So the 450's should be fine. The 2114 comes under a number of different names ... TMM314APLs are the same and are pretty widely available on the likes of eBay. Stuart.