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Forum Index : Microcontroller and PC projects : Just testing a Game-Mite concept
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Mixtel90 Guru  Joined: 05/10/2019 Location: United KingdomPosts: 6798 |
No reason at all as far as I know. Pinouts are different and LATCH is active high for 4021 but active low for 74HC165, I think. You have to bear in mind that the CD4021 predates common use of 3V3 devices. The spec at 25C with a 5V supply is <1V is zero and >3V is high. The noise threshold is 0.45 * Vcc = 2.25V with a 5V supply and 1.48V with a 3V3 supply. It probably works fine but it was never specified for 3V3 operation. EDIT: Just discovered that the CD4021BC has a supply voltage range from 3V to 15V. https://www.redrok.com/CMOS_CD4021BC_8-StageStaticShiftRegister_Fairchild.pdf Edited 2023-11-04 07:25 by Mixtel90 Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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stanleyella Guru Joined: 25/06/2022 Location: United KingdomPosts: 2129 |
The vero button pad with i2c is just for me and cut the board or use it for outputs. dunno but it should be ok when software decode buttons done. i2c easy connection. software is not familiar with 2 forum examples for which I'm grateful. pcb looked neater. |
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Turbo46 Guru Joined: 24/12/2017 Location: AustraliaPosts: 1611 |
You are right! The Intersil datasheet does not exactly specify a supply range but talks of 5, 10 and 15v only. The Texas Instrument sheet says 3 to 18v. The load pulse for the CD4021 is also nanoseconds so I was wrong about that too. I was going by what Tom says in his program: "The NES standard specifies a 12 micro-second pulse" That may be playing ultra safe. In that case I would stick with the devil you know the CD4021BC. Bill  Keep safe. Live long and prosper. |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6798 |
I had a further play last night and, if I've figured it out right, the traces for the 74HC165 are far simpler than they are for the CD4021. Not that it matters. :) The main objection to using it that I can see is the polarity of the Latch pulse. It seems to be slightly cheaper and slightly more available than the CD4021, I think. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| Volhout Guru Joined: 05/03/2018 Location: NetherlandsPosts: 4243 |
The CD4021 is NES controller stuff. So you can directly replace the chip with one of those controllers. The 74HC165 (see PIO training on this forum) uses different clock edge or latch pulse. The HEF4021 can also be used (old Philips part). Volhout Edited 2023-11-09 00:51 by Volhout PicomiteVGA PETSCII ROBOTS |
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