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Powertran Cortex

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    I've got a 9904 also made in Malaysia with identical markings apart from some of the numbers being different, so I'd cautiously suggest that these are good. Maybe e-mail the seller first and just say that you're aware there are some fake TI chips round at the moment and will he give a full refund if there is a problem.

    Stuart.

    Originally posted by mnbvcxz View Post
    I have seen on ebay tim9904 described as 8 to 3 line encoder, having read that components from utsource are sometimes fake, do you think this is worth a try?

    http://www.ebay.co.uk/itm/1209208399...84.m1438.l2649

    Thanks.

    Comment


      Christmas greeting to everyone. I'm lucky enough to have nearly 2 weeks off work so there's a real risk I might get round to buying sockets for my bare Cortex board ...

      Comment


        Go for it, Stuart! I may have to start on mine as well. . .assuming my five and seven year old boys let me have some "me" time. . .not to mention the wife!
        Enter My Mind At Your Own Risk!

        Comment


          The deed is done and most of the PCB hardware is now ordered. I'll try to order the ICs on E-bay over the next couple of days. Need to hide the credit card bill from the wife next month ...

          I'm planning on the following changes:

          (1) ZIF sockets for the three EPROMs. EDIT - scrub that idea. It looks as if the holes in the PCB for the IC pins are too small for the pins of a normal ZIF socket.

          (2) I'm not going to build the keyboard. I could probably get suitable key switches, but the hardware for the space bar may be a problem, and getting the exact set of labelled key tops is probably not reasonably possible. Instead I plan to control the Cortex from the PC through the RS-232 interface. May need to modify the EPROM code to change some Cortex keyboard scan codes to suitable PC Ctrl key codes.

          (3) I'm not going to fit the analogue PAL video hardware, instead I'm going to fit a TMS9918 which gives a direct composite output (just needs a pull down resistor) which works with my PC TV tuner card. I'll need to bend 3(?) IC pins out of the socket so I don't have to modify the PCB.

          (4) I'm going to power the board from a PC power supply unit, and have ordered an ATX extension lead that I can modify for the purpose.

          Jim: I haven't been able to order the following capacitors. Would you happen to have one of each kicking around? They're for the tape interface, which I don't plan to use other than confirming that it's working. C22 (330n), C24 (5n6), C23 (2n2).
          Last edited by Stuart; December 26, 2012, 04:03 PM.

          Comment


            Why not fit the F18A instead of the 9918?

            Comment


              A good idea ... but I haven't got the room in my little computer corner for another monitor, and I don't really want to have to shuffle monitor cables around whenever I want to use it.

              Comment


                Originally posted by Stuart View Post

                (2) I'm not going to build the keyboard. I could probably get suitable key switches, but the hardware for the space bar may be a problem, and getting the exact set of labelled key tops is probably not reasonably possible. Instead I plan to control the Cortex from the PC through the RS-232 interface. May need to modify the EPROM code to change some Cortex keyboard scan codes to suitable PC Ctrl key codes.


                Jim: I haven't been able to order the following capacitors. Would you happen to have one of each kicking around? They're for the tape interface, which I don't plan to use other than confirming that it's working. C22 (330n), C24 (5n6), C23 (2n2).
                Hi Stuart,

                Have you considered using a microcontroller to interface to a PS/2 PC keyboard? The output from the micro can be made to match the Cortex keyboard controller and you get the 'key-down' functionality for games etc. which is not easy to do using the RS232 port. I did it once just to prove the concept using an Atmel chip (they provide an Application Note that gives the circuitry and software as a foundation, so very easy to do: http://www.atmel.com/Images/doc1235.pdf).

                This would keep the RS232 port free to use to save/load programs to/from a PC using the PC Comms Util

                Dave.
                Last edited by tms9995; December 30, 2012, 08:59 AM.

                Comment


                  Originally posted by tms9995 View Post
                  Hi Stuart,

                  Have you considered using a microcontroller to interface to a PS/2 PC keyboard? The output from the micro can be made to match the Cortex keyboard controller and you get the 'key-down' functionality for games etc. which is not easy to do using the RS232 port. I did it once just to prove the concept using an Atmel chip (they provide an Application Note that gives the circuitry and software as a foundation, so very easy to do: http://www.atmel.com/Images/doc1235.pdf).

                  This would keep the RS232 port free to use to save/load programs to/from a PC using the PC Comms Util

                  Dave.
                  You're taking me out of my comfort zone there Dave, suggesting using something as modern as a microcontroller. One reason I do have for using the PC is that I have a little program to send text a character at a time from a text file down the RS-232, so I can 'save' by simply listing a program over the RS-232 then copying it into a text file, and 'load' by using the program to send it back again. You're right about the 'key down' functionality for games though.

                  Will hopefully try getting the Cortex running tomorrow if the last of the IC sockets arrive.

                  Stuart.

                  Comment


                    Originally posted by Stuart View Post
                    You're taking me out of my comfort zone there Dave, suggesting using something as modern as a microcontroller. One reason I do have for using the PC is that I have a little program to send text a character at a time from a text file down the RS-232, so I can 'save' by simply listing a program over the RS-232 then copying it into a text file, and 'load' by using the program to send it back again. You're right about the 'key down' functionality for games though.

                    Will hopefully try getting the Cortex running tomorrow if the last of the IC sockets arrive.

                    Stuart.
                    You're probably right. They can be a bit intimidating. So, to make it simpler, why don't you use the TMS99110 system you designed to act as a PS/2 keyboard interface? That would be cool!

                    I hear what you're saying about listing the file to and from the PC, but it's slow and can be clunky if the line expands to be too long. I think you should at least give the Comms Util a crack. It will take care of your machine code as well, since you can use the MONitor commands to save/load. It's not far off a Cortex with disks as far as performance is concerned.

                    Anyway, good luck with the Cortex build!

                    Dave.

                    Comment


                      Originally posted by Stuart View Post
                      I've got a 9904 also made in Malaysia with identical markings apart from some of the numbers being different, so I'd cautiously suggest that these are good. Maybe e-mail the seller first and just say that you're aware there are some fake TI chips round at the moment and will he give a full refund if there is a problem.

                      Stuart.
                      Probably too late now (I didn't realise there had been any more messages here, I must have missed an emailed notification) but that is the company that sold the fake TMS9909 chips.

                      Jim

                      Comment


                        Originally posted by Stuart View Post
                        Jim: I haven't been able to order the following capacitors. Would you happen to have one of each kicking around? They're for the tape interface, which I don't plan to use other than confirming that it's working. C22 (330n), C24 (5n6), C23 (2n2).
                        Sorry, as per my other message, I didn't realise things were happening here.
                        Do you still need these caps ?, I had to order 5's and 10's of most of them so should have spares.
                        Which parts list did you use, there were a lot of changes on the later Cortex 2 parts list.

                        Jim

                        Comment


                          Originally posted by Stuart View Post
                          You're taking me out of my comfort zone there Dave, suggesting using something as modern as a microcontroller. One reason I do have for using the PC is that I have a little program to send text a character at a time from a text file down the RS-232, so I can 'save' by simply listing a program over the RS-232 then copying it into a text file, and 'load' by using the program to send it back again. You're right about the 'key down' functionality for games though.

                          Will hopefully try getting the Cortex running tomorrow if the last of the IC sockets arrive.

                          Stuart.
                          Designs do exist on the net for using a PC PS2 keyboard and a small micro to create a parallel keyboard, I think they are used on the Apple 2 amongst others.
                          My day job is mostly based around PIC micros so given some spare time I can make a PIC based keyboard interface.

                          Jim

                          Comment


                            Originally posted by Jim Hearne View Post
                            Sorry, as per my other message, I didn't realise things were happening here.
                            Do you still need these caps ?, I had to order 5's and 10's of most of them so should have spares.
                            Which parts list did you use, there were a lot of changes on the later Cortex 2 parts list.

                            Jim
                            Yes please Jim, if you have spares. I'll try to send you a PM with my address.

                            Also, the DIN socket for the cassette - did you get one that fits the board exactly? The one I've got the two pins at the front of the socket don't match the spacing of the holes on the PCB, and the pins at the back are too big to go through the holes (but I could file the pins down a bit if need be). If you got one that matches exactly, where did you get it from?

                            Fired the board up tonight and it's working. Need to tweak the code to make it default to the RS-232 for input/output. More tomorrow ...

                            Stuart.

                            Comment


                              Originally posted by Jim Hearne View Post
                              Sorry, as per my other message, I didn't realise things were happening here.
                              Do you still need these caps ?, I had to order 5's and 10's of most of them so should have spares.
                              Which parts list did you use, there were a lot of changes on the later Cortex 2 parts list.

                              Jim
                              Parts list - I went with the Cortex II list and diagrams but checked and cross-checked everything and found several errors. Might be worth you and I comparing notes some time and producing an addendum.

                              Stuart.

                              Comment


                                When I was at college in 1982 I was flicking through a copy of an Electronics Today magazine lying on a bench and I saw these circuit diagrams for this rather nice computer - the Powertran Cortex. I was able to get the relevant issues together and photocopy the pages on the college photocopier. Those photocopies are still in a folder on a shelf above my head. Now, 30 years later, I finally have a working Cortex beside me. Working that is except for a few missing caps in the cassette circuit, and the VDP and video RAM which at the moment are somewhere mid-Atlantic ...

                                I got BASIC booting last night - 'booting' in terms of the TIME LED flashing away. And I've spent all day today trying to get the thing to default to input/output over the RS-232 interface to the PC. I thought I'd be able to just change the default UNIT value and bypass the code that does the EPROM checksum, but it's been rather frustrating as that didn't work. So I've spent the day programming EPROM after EPROM (I'm using a single 27C256 in an adaptor) trying this and that. I proved that the RS-232 hardware was working by getting the Monitor program (with the CRU base address changed) from my TMS9995 Evaluation module running.

                                Then I remembered that Jim had a problem with the RS-232 as well and checked back on his and Dave's posts. The DSR line on the TMS9902 was indeed sitting inactive at a logic 1. So strapped pin 20 to pin 6 on the back of the PCB ... except that the PCB seems wrong ... the 75189 RS-232 receiver input is connected to pin 19, and pins 19 and 20 don't appear to be connected as the circuit diagram suggests. So strapped pins 19 and 6 instead and DSR on the TMS9902 is now at logic 0. But still no joy. Scratch head. A slight tweak to the code ... There's a TB 27 followed by a JEQ in the RS-232 DSR section that tests the state of the DSR input. Changing the JEQ to a simple JMP so that the state of the DSR input is ignored, and my terminal program on the PC reports "CORTEX BASIC Rev. 1.1. 1982". Now the DSR input *should* be correct, so I'll have to try to see why it's not working.

                                I've also converted the BASIC source code and files so they will assemble as one using the Asm994a assembler (as opposed to assembling individually then linking). The assembler list file is useful as it gives you the actual address for each line of code.

                                And now, to bed ...

                                Stuart.

                                Comment

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