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22

According to Wikipedia, The unusual architecture of the 99/4 series is documented to be due to the failure of the 9985, an 8-bit processor which was being created specifically for the machine. When it was abandoned, the 16-bit 9900 was selected to replace it, and a great deal of "glue logic" had to be added to fit the processor into the existing design, ...


18

Now given that the TMS9900 has a 16 bit databus, it seems to me that they could have put all memory and all periphery on that bus. It would have saved the cost of the multiplexor, and made the computer a good deal faster too. Presumably it would have simplified the routing of the circuit board also. Yes it would - if the computer had been intended to be ...


10

However, the TI cartridges could also contain a different type of ROM called "GROM". Which I believe was "Graphics ROM". Jup, although, it wasn't really related to graphics at all. More due the fact, that its primary usage within the TI99/4 was to hold GPL code - which itself stands for Graphic Programming Language. There was also GRAM, if memory serves, ...


9

If you look at the description of the databus multiplexer e.g. here The TMS9900 being a 16-bit processor, it has 16 data lines and 15 address lines. However, only the console GROMs (>0000-1FFF) and the scratch-pad RAM (>8300-83FF) are accessed in this way. Peripheral memory in the range >2000-7FFF and >A000-FFFF is accessed via an 8-bit data bus,...


9

CRT screens used varying magnetic fields (from wire coils carrying a sawtooth-wave electrical signal) to deflect an electron beam and scan it across the screen. These fields extended outside the TV to some extent. If you had two TVs next to each other, being driven by signals that were at slightly different frequencies, the magnetic field from one TV might ...


8

Unless you had dozens of different types of TV's with a controlled test, it's hard to really quantify how good that RF modulator was (or how bad). Also, you said you don't remember what the third computer was. Are you sure you remember it having a better display? When I was a small child, I had a TI-99/4A and a Commodore 64C. Both of them were RF only. ...


8

Any cassette tape system which can utilize a standard cassette tape recorder can be plugged into any audio device, with sufficient quality, and will work. You can record saved files with any audio recording app and load it back in by playing it back. I know this is regularly done on the Apple II, Sinclair ZX Spectrum, and Tandy Color Computer systems, and ...


8

So my question is why the TI-99/4 had these two databuses. Why not put everything on a single databus? The TMS9900 CPU only has three on-chip registers, none of them being so much as an accumulator. I.e., every mathematical and logical operation occurs in RAM registers. From Wikipedia: Only the Program Counter, Status Register, and Workspace Pointer ...


5

According to jdv's answer to another question, cotton swabs and isopropyl (rubbing) alcohol will do the trick. Try to keep the alcohol away from plastics, use it sparingly and be gentle when you rub the dirt. His answer also says that "fancy contact cleaner" will work: For example, "CRC QD Contact Cleaner". Make sure you don't get the type used for ...


5

A pink pencil eraser is a reasonable contact cleaner for this sort of thing. Just scrub the black dots a bit and see if they will respond to softer pressure.


5

I always thought this was unique to the Atari until around 1984/5 when I saw a TI-99 at the local mall doing the same thing Well, similar but different (*1), as the Atari mixes the AUDIO-IN signal from the SIO port, which carries the left channel, with the sound output of the POKEY, while the TI inputs the (mono) cassette output into the TMS 9919, wh then ...


4

You seem to be describing a TV that wasn't fine-tuned to the Channel 3 or Channel 4 VHF signal coming from the TI-99/4A. Any computer or game using the RF modulator style of connection could suffer some kind of frequency drift. And cabling issues could often hamper reception due to impedance mismatching (visible as noise), standing waves (visible as multiple ...


2

But for some reason, you could only work with 28 sprites instead of the maximum of 32. So, what was the reason behind this? One reason may have been space. Of the 16 KiB RAM, build-in TI-BASIC uses 2 KiB for screen handling (including 80 bytes line buffer) (*1), leaving a bit less than 12 KiB for programm and data. For Extended BASIC it is essential to be ...


2

I have tried to save or load from a smartphone and PC. These don't record well. However the audio file from tape may be processed on PC. Audiotap and CS1er are examples of software for the TI. I have tried successfully to use an MP3 player (including through Bluetooth) to play wav files. A repossitory for wav files is at whtech: https://computerarchive.org/...


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