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mightydidz wrote: ↑Mon Dec 21, 2020 2:59 pm
According to 74'138 datasheet it would be Y0 output?
Yes.
The eight latches of the ’HCT373 devices are transparent D-type latches. While the latch-enable (LE) input is high, the Q outputs follow the data (D) inputs. When LE is taken low, the Q outputs are latched at the levels that were set up at the D inputs.
Oh, hm. You won't be able to use most transparent latches after all, because the 74'138 emits low when the correct inputs are selected, but the 74'373 holds the current value when its +LATCH input is low.
I'm still uncertain about the other latch inputs/outputs. How do I use them for my application?
74HCT374 is an octal positive-edge triggered D-type flip-flop with 3‑state outputs. The device features a clock (CP) and output enable (OE) inputs. The flip‑flops will store the state of their individual D-inputs that meet the set-up and hold time requirements on the LOW-to-HIGH clock (CP) transition. A HIGH on OE causes the outputs to assume a high-impedance OFF-state. Operation of the OE input does not affect the state of the flip-flops. Inputs also include clamp diodes, this enables the use of current limiting resistors to interface inputs to voltages in excess of VCC.
Using Y0 on CP?
What exactly do I connect to Dy and Qy?
Where do PRG-A18 comes into play?
'374 would be fine, but overkill. That has 8 bits of latch, you only need 1.
Using Y0 on CP?
Yes, because /Y0 will go high when the inputs are no longer correct (e.g. /ROMSEL rising), which is the same time that the various discrete logic mappers capture the data bus.
What exactly do I connect to Dy and Qy? Where do PRG-A18 comes into play?
Think of it as identical to an normal UOROM board. You're just converting a plain UOROM board into one that can play a 512KB game.
The UNROM, UN1ROM, and UOROM boards contain a 74HC161 binary counter used as a quad D latch (4-bit register) and a 74HC32 quad 2-input OR gate to make one bank always visible
Do I also need to have one bank always visible?
'374 would be fine, but overkill. That has 8 bits of latch, you only need 1.
mightydidz wrote: ↑Mon Dec 21, 2020 4:53 pm
Isn't a UOROM using quad D latch and quad OR gate to bank PRG up to 256KiB?
Yes? How do you think it works?
Do I also need to have one bank always visible?
Yes, that's why I compared it to UNROM.
Would something like SN74LVC1G374 would be more reasonable? Or maybe SN74LVC1G79. Do I need an /OE?
Just based on cost and ease of assembly. Both of those are fine. You don't need an /OE pin, although it might let you replace the extra OR gate with a resistor pullup.
Its been a while since I worked on this project but I finally received my prototype pcb adding those 3 extra components 74'138, 1G79 and 1G32.
It works with regular japanese rom and some other 159 mapper games, but not with the english Knight Gundam Monogatari. https://www.romhacking.net/translations/5482/
I tried with 24C01 and 24C02 eeprom but same results, only a yellow screen.
Here is my schematic if someone want to take a look at it.
Any idea if its the rom or the schematic?
Thanks