74LS257 DATASHEET PDF

74LS datasheet, 74LS pdf, 74LS data sheet, datasheet, data sheet, pdf, Fairchild Semiconductor, 3-STATE Quad 2-Data Selectors/Multiplexers. These Schottky-clamped high-performance multiplexers feature 3-STATE outputs that can interface directly with data lines of bus-organized systems. With all but. 74LS datasheet, 74LS circuit, 74LS data sheet: FAIRCHILD – 3- STATE Quad 2-Data Selectors/Multiplexers,alldatasheet, datasheet, Datasheet.

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Users browsing this forum: Google [Bot] and 0 guests. Mon Dec 31, 3: TTL Here I come. Thu Feb 15, 1: Just to sum up a few things: From the datasheet, 82S propagation delay input to output is 35ns typ.

Hitachi Semiconductor 74LS Datasheet.

Should be taken into account when trying to run a C64 with a W65C Fri Feb 16, 8: Got the timing parameters for 74xx chips from there: Fri Feb 16, If this works, we need to come up with a plausible theory datasheef, what will take some time. If this fails, we need to come up with a plausible theory why, what will take some time.

Datasheet Feb 19, Thanks for all the comments Dieter! Sun Aug 05, 2: I had left off with stable operation at 20MHz, wondering if that could be bettered.

Sun Aug 05, 3: The Datxsheet will allow a very gradual increase of the clock-rate, which is very handy.

Unfortunately, it is also VERY sensitive to voltage changes, and that’s been a problem. I was surprised to discover a significant voltage drop between my workbench PSU and the SBC, and the gap got wider with higher clock-rates. The VFO will be used seldom enough that it should be practical to give it its own 9V battery and a 78L05 regulator or even an adjustable LML both being in a small TO packageso it won’t be affected by the computer’s power-supply voltage.

Sun Fatasheet 05, 4: Mon Aug 06, 1: Ground is still common, but not Vcc. All voltages are referenced to ground though, and a DMM would show zero ohms from any ground pin to any other ground pin. This results in a potential threat which you may choose to address. Or not — there’s a reasonable chance you can ignore the issue and get away with it. Anytime the VFO power supply is substantially higher than the SBC power supply which could happen during powerup or powerdown you can encounter unexpected current flow.

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IC Datasheet: 74LS257

If the VFO output is strong enough it’ll exceed the fairly tiny current-carrying capability of the input-protection diode and destroy it. Otherwise you could consider other strategies. Or add 74ls527 external input-protection diode Schottky type on the SBC to help the internal diode carry the current. Finally, a low value series resistor 20 or 30 ohms? Mon Aug 06, 6: The VFO kind of falls into the category of test equipment to be connected temporarily; so from that perspective, you could connect it only after both the VFO and the SBC are powered up, then press the SBC’s reset button.

If there’s a doubt though, note that if you use only ohms, a logic output of nearly 5V, minus a Schottky diode drop, divided by ohms is still over 40mA; so I would make it perhaps ohms, and put a 47pF or pF across that resistor so the slew rate at the load doesn’t get too slow. Let’s say the load were 30pF. For CMOS thresholds at. You’d definitely want that capacitor across there 74,s257 prevent that slowing. WDC’s data sheets call for a clock-input rise and fall time of 5ns or better. Mon Aug 06, 8: Look at what that little CPU did!

Congratulations to your success!! Page 29 of Previous topic Next topic.

Here is the I say nearly because I see slight differences between them, several of which are 10ns variations, and may simply be artifacts of the sampling rate Mhz. I do see the address lines reacting more quickly after AEC changes state.

This is most visible during the second write pulse. Even so, I tried delaying the AEC signal with a 1k resistor just for kicks — no luck. I may try other values just to see, but it’s a guessing game at best.

74LS257 Datasheet

Darn, this one is proving to be very stubborn! You do not have the required permissions to view the files attached to this post. The first line of defence was to improve cabling. That helped narrow the voltage gap, so I felt the CPU was more easily able draw the additional power it requires at high clock-rates. The simplest fix was to build an small wait-state adapter board to fit the empty 65C02 socket of the SBC. This socket goes unused when the TTL CPU is installed, and it conveniently has all the signals we need for wait-stating.

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I used dwtasheet wait-state circuit we discussed earlier in this thread to insert datasheeet or two datasheet when A15 goes high, as follows: That leaves precious little time for address decoding before the rise of PHI2, and any additional delay for clock-stretching or RDY logic will easily exceed the time available. That allows datasneet of time, in fact, and this circuit requires only a single gate delay between address logic and RDY, which is about as crisp as you can get.

I tested the circuit with the 65C02 on a breadboard and it worked perfectly. It turns out RDY took effect one cycle too late! It was a bug, and one that had gone unnoticed to this point. This assumes the processor setup time is met. This again assumes the processor control setup time is met. Datasheef verified proper operation of the RDY circuit, and other preparations having been dataheet, it was time for the big moment Now that seems like a lot of work and trouble for just 1 MHz above the previous record, but so be it.

Ok, back to more testing with the C64! Cheers for now, Drass Datashee do not have the required permissions to view the files attached datasbeet this post. Congratulations on the success!

Not sure how one goes about mixing two power sources like this. A very gratifying result, especially given the cycle-accurate constraint. But first, there is still that C Having multiple power supplies is common although not so much with circuits. Having a separate stable voltage source for the VFO is a great idea. The problem was entirely the result of a silly error. The C64 booted without a problem. Now here is one of the original objectives of the project as outlined back in The game is called Neoclypssort of a homage to Defender on the C Major milestone, major success – congratulations Drass!

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