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Stuart last won the day on September 18 2016

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  1. Actually, looking at the SuperCart construction notes, there's already a resistor between pins 27 and 28. If you've built the SuperCart using a TI game cartridge as per http://www.mainbyte.com/ti99/supercart/supercart_4bank.html, then you should be able to write protect the RAM simply by inserting a switch in the wire between the 3rd edge connector pin and pin 27 of the RAM.
  2. You'll either need to bend pin 27 so it doesn't go into the socket, or cut the trace to the IC pin 27 on the PCB. Bending the pin out of the socket might be easier then it leaves your PCB pristine. You might find it best to only change the switch with the console powered off, then you don't get a problem with the RAM possibly being corrupted when the switch output is connected to neither input for a couple of milliseconds as the switch changes position. Should be a simple schematic attached.
  3. Pin 27 is /WE. So have a switch in-line with the connection to that pin, plus a ~1K resistor connected between that pin and pin 28 (+5V) to ensure that /WE is pulled high when the switch is in the 'off' position.
  4. In bitmap mode you can display text on a 32 character by 24 row grid - so easy to add labels if the tick marks happen to align with the character grid (or possibly tweak your axis scales so that they do align). If they don't align, then you could define the label text character bitmaps as stationary sprites which can be positioned with pixel accuracy.
  5. I wouldn't say that 14K of RAM free for program and variables restricts it to "very very small programs"!
  6. It's in the manual - section (Appendix A of the manual contains an alphabetical list of BASIC keywords which is handy for finding where things are described.) Yes, I ported Cortex BASIC over from the original Cortex version.
  7. Cortex BASIC does, not sure about RXB. Scroll down to the bottom of the following page for an example: http://www.stuartconner.me.uk/tms99110_breadboard/tms99110_breadboard.htm
  8. http://www.unige.ch/medecine/nouspikel/ti99/download.htm#disass A couple of headings down from the top of the page, "The disk controller card ROM" Also appears to be the code for DSRLNK a bit further down the page (ea3.txt)?
  9. In addition to Tursi's reply above, take a look at https://archive.org/details/COMPUTES_Beginners_Guide_to_C64_Sound_1984_COMPUTE_Publications_a. All the addresses and program listings are for the C64 so you'll have to convert them to TI-99 addresses, but it contains valuable info about how the SID chip works. Here's the SID chip playing on my TM990 system:
  10. If SB uses the MSB of both R1 and R4, your LI R4,>30 needs to be LI R4,>3000 to put the >30 into the MSB?
  11. What you might want to consider is displaying both hex data and ASCII on the same screen, something like below. Very useful for spotting text strings within the data. (Noticed a little typo in your video - HEXIDECIMAL should be HEXADECIMAL)
  12. Get yourself a copy of the TI-99 circuit diagram if you haven't already (Google will find it for you). Find the TMS9901 on the circuit diagram and look at the inputs from the keyboard - pins P5 and /INT3 - /INT10. With the keyboard disconnected, check that each of these is being pulled to +5V. There's a pull-up resistor and a capacitor on each line that might be causing the problem. The TIM9904 clock chip has no bearing on the keyboard problem.
  13. Pretty much all the 9901 pins are already used, but it's fairly easy to add a second 9901 to the console by piggybacking it on the existing one and mapping it to unused CRU address (>0400 or >0800?). If you've got a RAMDisk in your system and have the source code for the DSR, then it is fairly easy to add a new device entry (so you don't need to mess around with the hardware to support a separate DSR just for the clock), and then add the software to support opening and reading/writing to the clock. That's how I added support for a parallel keyboard interface many many years ago.
  14. Did you change the 9904 (the clock chip) or the 40-pin 9901, which interfaces with the keyboard?
  15. http://www.unige.ch/medecine/nouspikel/ti99/eeproms.htm#console
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