74HC Datasheet, 74HC stage Binary Counter Datasheet, buy 74HC, 74HC pdf, ic 74HC description/ordering information. The ‘HC devices are stage asynchronous binary counters, with the outputs of all stages available externally. A high. Data sheet acquired from Harris Semiconductor. SCHSD. Features. • Fully Static Operation. • Buffered Inputs. • Common Reset. • Negative.

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This could be interesting. I’m already bummed about the color thing In the schematic above, the ‘ counters increment the address on the rising edge of the clock, while the ‘ d-flop captures the data from the last address before it changes.

Did I miss something on the ripple counters? If I’m reading the datasheet correctly, the maximum delay from clock edge to valid outputs is Since it’s a ripple counter, Q0 flips, then Q1, then Q2, etc, so we have to add all the delays so see how long it takes for the address to settle to the next value.

The row address can be updated from the horizontal sync. In this case, it’s not memory but registers. In the store-each-dot-period-as-a-byte plan, this is trivial – I datashet full and easy control of all the singals on on a per-dot basis.

All these numbers involving multiples of propagation-delays are making me question even further how I got the ol’ LCD controller running. If I were going to build a bunch of these, I’d try harder to get the 74HC to work. Let’s run the numbers, using a 15pF load: Interesting discovery upon looking back This would work – with the 12ns SRAM access time, still way under the 40ns cycle time. This also ignores the fact that two 74HCs need to be chained to generate the bit address: Here’s a simplified schematic of the guts of the VGA framebuffer it ignores the reset and connections between the two ”s required to generate 19 bits of address.



Doesn’t look datasheeh – although the typical 21ns 6V or 25ns 4. About Us Contact Hackaday. Add in the 12 ns access time of datasheet SRAM, and we’re definitely over budget. The dot clock is I have a tube of 50 MHz cans around here that I could divide down, but since I have to order parts for this thing anyway, I might as well pick up the exact frequency for a few bucks.

I have to go take them out of my shopping cart now: Maybe a fast external counter for the lowest 4 or 8 bits, and the PIC generates the upper ones? If I were making more than a one-off project, I think the 25 MHz idea might be the way to go.

VHC to the rescue? The 74VHC is another candidate – it has twin 4-bit counters in a package, so three 74hf4040 would be necessary.

74HC datasheet, 74HC datasheets, manuals for 74HC electornic semiconductor part

Synchronization is an issue, but it’s worth thinking about – maybe if the PIC runs from the external Dattasheet haven’t used VHC logic before, but keep seeing it around.

Even if you could output a new address every cycle, that’s still only about half of the Monitors can handle some clock frequency variations. I saw the 25 MHz trick in your terminal project – good to know.


Surely the 74VHCwith its Mhz typical max clock frequency will do the job! Synchronous counters use extra logic to form the next state from the previous one directly, without waiting for clocks to ripple through, so the outputs settle faster.

For Qd the fourth bitthe typical tpd is given as 8. I spent the afternoon re-working my ugly SOIC adapter board designs to reduce the ground-connection impedance and add on-board bypass caps. So, with two of them connected to dtaasheet 19 bits of address, the tpd from the clock edge to the MSB settling is: I’m going to ignore those timing calculations for the moment next log because there’s an even bigger problem here – it takes too long for the address to settle.

It’s a shame, because the ‘ packs bits into a single package. Sign up Already a member? What about using the fastest PIC available and bitbanging the address lines? Musta been a bunch of pixie-dust in there, or a poor memory of datasyeet years ago. So, what the heck, I’ll look at timing before slapping something together.

I can hook one to the four-channel scope and have a look at the delays between the 74hc400 and successive bits. I started with the VHC part this time: I need 5 of them, which sucks. That should relax some timing as your MSB are no longer rely on the propagation from the lower bits.