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Powertran Cortex

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    Originally posted by Jim Hearne View Post
    A quick look at your PCB and I would say you need more 0.1uf decouplers, at least one for every chip, as close between 0v and 5V as you can get them.
    OK, I'll try to fit some more in. I'm using 1uF tantalums to decouple, is that a good choice? Also two 100uF mini elco's thrown in for good measure. This seems to work out okay on the breadboard. Or am I being silly?

    Originally posted by Jim Hearne View Post
    Silly question, where does the power connect ?
    Power is drawn from the USB host. The circuit should draw less than 500mA. For the USB bridge I use see:
    http://www.elektor.com/ft232r-usb-se...-bob-110553-91
    This power source has worked well on the breadboard. Perhaps I need to add a 5.5V zener diode from Vcc to GND as a circuit protector.

    Thanks for your input!

    Comment


      Originally posted by pnr View Post
      OK, I'll try to fit some more in. I'm using 1uF tantalums to decouple, is that a good choice? Also two 100uF mini elco's thrown in for good measure. This seems to work out okay on the breadboard. Or am I being silly?

      Power is drawn from the USB host. The circuit should draw less than 500mA. For the USB bridge I use see:
      http://www.elektor.com/ft232r-usb-se...-bob-110553-91
      This power source has worked well on the breadboard. Perhaps I need to add a 5.5V zener diode from Vcc to GND as a circuit protector.

      Thanks for your input!
      Decouplers are normally 0.1uf Ceramics to filter the high frequency noise from the logic.
      I'm not sure if tantalums are as good at high frequencys though they are much better than electrolytics are.
      Leave the Electrolytics you have in for low frequency filtering.

      I use USB to TTL serial cables like these a lot at work.
      http://uk.farnell.com/ftdi/ttl-232r-...ire/dp/1740364
      They are great for hooking up directly to a TTL serial port on a micro.

      Can i suggest putting a couple of pads for a terminal block or a connector on the 5V rail, also maybe some pads for the serial port.
      It would give people some other options if you end up selling any of the pcbs.


      A diode or power Zener across the supply is always a good idea.
      It's about the first thing i connect on any prototype, especially if it's being powered from a bench supply with some test leads.
      They are known as dickhead diodes where i work.

      Jim

      Comment


        Things that are always useful on any microcomputer board are :

        Standard Power Jack
        power ON LED
        ON/OFF switch
        Safety Fuse ?? perhaps
        7805 voltage regulator

        Also it's good to use standard connectors like 9 pin D type for RS232 .. though the RS232c standard didn't specifiy any perticular connector the 9 pin D Type became standard !

        Comment


          Most Microcomputer boards tend to need :

          A Generic 2.1mm power Jack so a low cost PSU can be attached 9/12V ?
          7805 Regulator
          Power on LED
          Safety Fuse...Perhaps but the 7805 should be enough safety ?
          ON/OFF Switch

          Standard D-Type connectors for things like RS232 ?

          Comment


            Originally posted by ti99/4a View Post
            Most Microcomputer boards tend to need :

            A Generic 2.1mm power Jack so a low cost PSU can be attached 9/12V ?
            7805 Regulator
            Power on LED
            Safety Fuse...Perhaps but the 7805 should be enough safety ?
            ON/OFF Switch

            Standard D-Type connectors for things like RS232 ?
            Thank you for your input! The mini cortex is designed to have a USB interface, hence the D type connector is less appropriate. USB also provides a regulated 5v power source, that's why you don't see a 7805 or equivalent regulator. The power led is already there.

            I think I will add a header to accommodate other interface wishes.

            Comment


              Originally posted by Stuart View Post
              U10. Feel a bit uncomfortable that CRUCLK isn't involved in deriving the /CE. I guess though that if /MEMEN is high then it must be a CRU cycle (or an external instruction, which you aren't using by the looks of things).

              Stuart.
              This comment was naging me and I just realised why: Unix and xinu do use the idle instruction. Considering the very partial cru adres decoding I guess that I was lucky that the breadboard verslons worked. i'll add a ls138 external instruction decoder to the mini cortex.

              Comment


                Originally posted by pnr View Post
                This comment was naging me and I just realised why: Unix and xinu do use the idle instruction. Considering the very partial cru adres decoding I guess that I was lucky that the breadboard verslons worked. i'll add a ls138 external instruction decoder to the mini cortex.
                Have you got room to add another GAL, and implement it in that? Then have some spare GAL inputs/outputs for future tinkering. And as you're decoding the external instructions, is it worth using /LREX to do the single step and /CKON/CKOFF to switch the memory mapper on/off (with the spare flip-flop), as per the Cortex? Will need to do some rework of the PCB of course. ;-(

                Comment


                  Originally posted by Stuart View Post
                  Have you got room to add another GAL, and implement it in that? Then have some spare GAL inputs/outputs for future tinkering. And as you're decoding the external instructions, is it worth using /LREX to do the single step and /CKON/CKOFF to switch the memory mapper on/off (with the spare flip-flop), as per the Cortex? Will need to do some rework of the PCB of course. ;-(
                  Not sure I can fit a 24 pin part, a 16 pin part should fit. I think I need the spare flip-flop for the LREX interface als well, right? What is beter in that case, LREX or CKON/CKOFF? I would guess the former as there is no vintage software that uses the cortex mapper?

                  Also, I'm more and more tempted to shift most stuff over to the left and squeeze in an F18A socket in between the CF card and the CPU/MEM chips.

                  Comment


                    Something slightly off-topic :

                    *** Sourcing ICs from China *** an idiot's guide :

                    some of you may have noticed that I was selling some TMS9900 kits on ebay ? My little experiment to get people interested in hardware design etc has now finished !

                    These kits of ICs where sourced from two Chinese suppliers : G&C supermarket and Funkward-tech. I didn't test any of these ICs myself (though the supplier said they had, ...as they would !) However I did send a small sample to Stuart and he found most to be OK ? Bizarley the ICs from G&C looked like brand New (NOS) where those from Funkward-tech were clearly pulls.

                    I know a lot of people have problems with sourcing these ICs from China , but I've found them to be pretty good, the few DUFF ICs I received where promptly resent and replaced with new..

                    If anyone needs help with sourcing ICs please just ask.

                    Comment


                      Below is a rough guide to the prcies I paid for some ICs, this may be useful when costing a project ?

                      Approximate wholeslae price for some common ICs

                      Wholesale prices:


                      CPUs

                      TMS9900 $3.0 each
                      TMS9995 <$7.0 each
                      TMS99105 <$20 each

                      TMS9901 $2.50 each
                      TMS9902 $2.0 each
                      TIM9904A $2.50 each

                      TMS9911 DMA $2.50 each
                      74LS61x Memory Mapper $2.50 each

                      TMS FDCs <$10 each .. ask for price
                      TMS9909 / TMX9909
                      TMS2797 FDC

                      Static RAMs (DIP)

                      HY6264 8Kx8bit 70ns/100ns $1.0 each
                      HY62256 32Kx8bit 70ns/100ns $1.0each
                      HM628128/TC551001/KM68000 128Kx8bit 55ns/70ns/100ns $1.0 each
                      KM684000/HM628512/K6T4008 512Kx8bit Static RAM 70/55ns $3.50 each

                      Static RAM (SDIP)

                      UM61256 15ns DIP <$1.50 each
                      UM61512 15ns DIP <1.50 each

                      NVSRAM (DIP) : DS1250/DS1245 etc
                      32Kx8bit / 128Kx8bit /512Kx8bit $2.0 each


                      EPROMs/EEPROMs

                      27C32 DIP <1.0 each 120/100ns
                      27C64 DIP <1.0 each 70/120/100ns
                      27C128 DIP <1.0 each 70/120/100ns
                      27C256 DIP <1.0 each 70/120/100ns


                      (DIP & PLCC)
                      W27C512 64Kx8bit 45ns DIP/PLCC $1.0 each
                      W27C010 128Kx8bit 70ns DIP/PLCC $1.0 each
                      W27C020 256kx8bit 70ns DIP/PLCC $1.0 each
                      29F040 512kx8bit DIP/PLCC $3.50 each PLCC $1.0 each

                      Video Processors

                      V9958 DIP64 <$5.0 each
                      D72020/D7220 DIP40 $2.0 each
                      V6366 PLCC68 $3.50 each
                      EF936x GDP DIP40 <$15.0 each
                      R6545 DIP40 $2.0 each
                      V9990 Surface Mount <$20.0 each


                      TMS4465/D41464 100ns DRAMs $0.75 each


                      Sound Chips

                      SN76489 DIP16 $0.50 each
                      SAA1099 DIP18 <$1.50 each
                      AY-3-8910 DIP40 <$2.0 each
                      YM2149 DIP $2.50 each
                      YM3812 DIP $1.50 each


                      PIO
                      8255 PIO DIP40PLCC44 $2.0 each : PLCC44 ones $1.0 each


                      MCUs

                      AT89C205 DIP $0.75 each
                      ATMega88 DIP $1.50 each




                      GALs/CPLDs


                      GAL22V10/GAL16V8 etc $1.0 each
                      EPM7128SLC84 $2.0 each
                      EPM7160SLC84 $10.0 each
                      EPM7064SLC4 ask ?

                      Comment


                        Originally posted by pnr View Post
                        Not sure I can fit a 24 pin part, a 16 pin part should fit. I think I need the spare flip-flop for the LREX interface als well, right? What is beter in that case, LREX or CKON/CKOFF? I would guess the former as there is no vintage software that uses the cortex mapper?

                        Also, I'm more and more tempted to shift most stuff over to the left and squeeze in an F18A socket in between the CF card and the CPU/MEM chips.
                        Ah, LREX does need a flip-flop by the looks of things. So we're a flip-flop short. If you used it for LREX, then the code for the single-step is just a simple LREX rather than the (6?) or so lines of code you posted earlier? Is that a benefit?

                        Yes please for the F18A socket. Have you checked out the F18A website to see which pins you need connected?

                        Comment


                          Is that a benefit?
                          A marginal one, but so is CKON/CKOF. Which is preferable?

                          Yes please for the F18A socket. Have you checked out the F18A website to see which pins you need connected?
                          Yes. Not very many.

                          Comment


                            Originally posted by lezanderson View Post
                            These kits of ICs where sourced from two Chinese suppliers : G&C supermarket and Funkward-tech.
                            My experiences with G&C have been good as well.

                            Comment


                              Originally posted by pnr View Post
                              A marginal one, but so is CKON/CKOF. Which is preferable?
                              If it were mine, I'd use the flip-flop for LREX single stepping. The mapper controlled through the CRU latch. As you said before, there is no existing software that uses the mapper.

                              Comment


                                With a bit of Tweaking it could be modified into a Tomy Tutor ??

                                Originally posted by pnr View Post
                                Here are a draft schematic and a PCB design for the "Mini Cortex". I have a little room left over on the PCB. I've considered adding further memory protection (futile), adding an ethernet chip or an F18A. For the latter I'm not so much interested in the 9918A part, but I find the embedded 9900 GPU intriguing and an F18A may serve as a handy development board to prototype an FPU for the 99105 project. On the other hand, mission creep is usually a progress killer.

                                Jim, Stuart and Ksarul, I would appreciate your constructive critique of the design and PCB (it has been 35 years since I last did a PCB and those were simple, hand-drawn affairs).

                                Paul

                                Comment

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