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Mark1960 · 7th Jul 2021, 12:09 am

Just thinking about possible replacements of the 74ls395.

74ls163 is a possible. This is quite close to the pinout of the 74ls395 and might only need a simple mod to the wiring. The 74ls163 is a counter, but could be used as a latch if load input is held low and this would latch data on the rising edge at the end of NADS. There is still plenty of time in the rest of the bus cycle for any modern sram even with the scmp running at double the clock frequency.

74ls173 is also a good possibility, though the wiring mod is a bit more involved. The 74ls173 is also rising edge triggered but also has the advantage of a positive logic reset input, which could be driven by NENIN so the ortonview or mk14 vdu would force page 0. I also have the option of 74hct173 to reduce the load on the data bus.

74ls193 would give active low gated transparent latch with positive logic reset, though I don’t think I have any. I might have 74ls192 and although this is a bcd type I think that would only make a difference if the count function was used.

7th Jul 2021, 12:09 am	#44
Mark1960 Octode Join Date: Mar 2020 Location: Kitchener, Ontario, Canada Posts: 1,297	Re: Multiprocessing SCMPII on MK14 Just thinking about possible replacements of the 74ls395. 74ls163 is a possible. This is quite close to the pinout of the 74ls395 and might only need a simple mod to the wiring. The 74ls163 is a counter, but could be used as a latch if load input is held low and this would latch data on the rising edge at the end of NADS. There is still plenty of time in the rest of the bus cycle for any modern sram even with the scmp running at double the clock frequency. 74ls173 is also a good possibility, though the wiring mod is a bit more involved. The 74ls173 is also rising edge triggered but also has the advantage of a positive logic reset input, which could be driven by NENIN so the ortonview or mk14 vdu would force page 0. I also have the option of 74hct173 to reduce the load on the data bus. 74ls193 would give active low gated transparent latch with positive logic reset, though I don’t think I have any. I might have 74ls192 and although this is a bcd type I think that would only make a difference if the count function was used.