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ortek_service · 16th May 2021, 2:36 pm

Yes, it does appear that it's a PMOS device (Some of the General Instruments ones also needed voltages other than just single +5V).
And +5 - (-12V) = 17V, so would fit in with that voltage range (rather than slightly-narrower Intel total 15V difference).
PMOS is inherently 'Positive-Ground', so often has Vss (Usually 0V/Ground on later NMOS & CMOS) connected to highest +5V voltage, and other supply pins are negative relative to that. But the datasheets can sometimes be rather unclear over this.

This encoder IC does seem to also have a 0V 'reference' pin as well - Whereas some like the original NS SC/MP-I CPU, and early EPROM's didn't actually have a 0V pin (So must have internally-biased their outputs at levels to give the standard 0V/ 5V 'TTL' levels that most on-board data-buses ran at).

Some slightly-later EPROM and DRAM IC's, were 3-rail devices, so as well as using +5V & 0V, these also needed 2 extra supplies - Often instead using +12V and -5V to get 17V total.

16th May 2021, 2:36 pm	#179
ortek_service Octode Join Date: May 2018 Location: Northampton, Northamptonshire, UK. Posts: 1,440	Re: The Transam Triton Personal Computer Yes, it does appear that it's a PMOS device (Some of the General Instruments ones also needed voltages other than just single +5V). And +5 - (-12V) = 17V, so would fit in with that voltage range (rather than slightly-narrower Intel total 15V difference). PMOS is inherently 'Positive-Ground', so often has Vss (Usually 0V/Ground on later NMOS & CMOS) connected to highest +5V voltage, and other supply pins are negative relative to that. But the datasheets can sometimes be rather unclear over this. This encoder IC does seem to also have a 0V 'reference' pin as well - Whereas some like the original NS SC/MP-I CPU, and early EPROM's didn't actually have a 0V pin (So must have internally-biased their outputs at levels to give the standard 0V/ 5V 'TTL' levels that most on-board data-buses ran at). Some slightly-later EPROM and DRAM IC's, were 3-rail devices, so as well as using +5V & 0V, these also needed 2 extra supplies - Often instead using +12V and -5V to get 17V total. Last edited by ortek_service; 16th May 2021 at 2:44 pm.