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Another Gigatron TTL in Finland

Posted: 17 Jul 2021, 16:36
by veekoo
I had to try to make a DIY kit from budgetronics. Lack of skills probably didn't get it all working so ended up using it as spare.

I ordered second one "Fully Assembled Gigatron TTL" from ebay and got it at reasonable price. When it arrived it was missing U39 serial input IC and another mail was coming with 74HCT595 later on.

Well I had the spare parts and took SN74HC595N, I was able to get blinkenlights, power on led, startup sound and main screen booting.

Long story short I had 3 keyboards at what 2 seemed compatible with PS/2 standard and I tried them but nothing happend. No signal lights at keyboard otherwise system seemed ready to accept commands.

Seller said it seemed normal operation because of missing the right IC chip and my chip needed 1N60P diodes and the board had BAT42 instead. Actually diodes looked pretty much the same as in my failed pcb.

Probably in question is some signal level matching or timings what I understood. Seller seemed sure of things so I have meen mostly waiting customs to send me my letter.

Re: Another Gigatron TTL in Finland

Posted: 18 Jul 2021, 15:50
by veekoo
I found this searching to what is different sn74hc595n and 74hct595:

”The 74HC595 operates in a voltage range of 2-6V, while the 74HCT595 operates within a narrower range of 4.5-5.5V. Although the 74HC595 can operate in a wider voltage range, it has a dramatically higher propagation delay than the 74HCT595. The 74HCT595 has a propagation delay just over a quarter of the 74HC595’s delay length—63 nanoseconds compared to 240 nanoseconds. This shorter delay means long delays are less likely to build up over time, which could cause an overall slowdown in an electronics project. A slowdown in a shift register, since its main function is to handle data, could be disastrous to computational speeds.”

Re: Another Gigatron TTL in Finland

Posted: 21 Jul 2021, 10:04
by veekoo
I had spare Pluggy McPlugface for ROM v5 (from tindie) and for just spending my time I decided to solder it togeather.

For my total suprise it seemed to work with SN74HC595. Probably this fully assembled version Pluggy McPlugface needs 74HCT595 - this does not.

Keyboard and everything works fine. Almost flawless operation except 3 dead big pixels at start screen. Didn’t come to my mind first that error might be in Pluggy McPlugface. Happy now. ;)

Re: Another Gigatron TTL in Finland

Posted: 21 Jul 2021, 10:55
by veekoo
Some operational pictures