Which latch to use? 74HC574 or 74HCT574

[Anthony Ortiz]

I'm looking to have my Raspberry Pi communicate with the Apple IIe via a peripheral slot and have decided that the "bus" I'm going to use to interface them both is the 574. I have some 374's in front of me but I much prefer the pin arrangement on the 574. My question is, should I use the CMOS or TTL logic level version? Also, what level converter would you guys recommend for 3.3 -> 5 and vice-versa?

[Anthony Ortiz]

Never mind which latch to use, mdj answered this nicely on march 8th in thread "what hardware is missing from the apple II"; his recommendation is to go with the TTL version.

That leaves my question on level translator open and I'd appreciate some advice from the experts.

Cheers!

Anthony

[cb meeks]

Post by Anthony Ortiz
I'm looking to have my Raspberry Pi communicate with the Apple IIe via a peripheral slot and have decided that the "bus" I'm going to use to interface them both is the 574. I have some 374's in front of me but I much prefer the pin arrangement on the 574. My question is, should I use the CMOS or TTL logic level version? Also, what level converter would you guys recommend for 3.3 -> 5 and vice-versa?

I don't know what conclusion you came to but I thought I'd mention some advice I got from the 6502 forums.

Some of those guys have been using 74LVC244A for voltage conversions. You can power it with 3V3 but the inputs are still 5V tolerant.

[Anthony Ortiz]

Okay so that will handle 5 -> 3, but what about 3 -> 5? Any chips that do both?

[Anthony Ortiz]

Okay, some more head scratching and google searching I discovered that the 74HCT series (the T for TTL is important here) will do the level transformation needed from 3.3v and register as the appropriate logic 0 or 1. This means the 74HC574 will work for uni-directional communication from the 3.3v Pi to the 5v Apple II bus. Now what I need is to go from 5v to 3.3v and I believe the 74HC4050 fits the bill, though I wish they would make them octal instead of hex.

Would someone please confirm or deny my findings?

Thanks!

[Anthony Ortiz]

Darn, that won't do... I need it to be three-state so I can make it float. So hard to find an IC when I don't know the part numbers or terminology lol!

[Anthony Ortiz]

Okay I think I got it now... SN74LVC245A octal bus transceiver with 3-state outputs lets me read from the 5v apple ii bus to the raspberry pi 3.3v GPIO and float it when not in use. Transceiver is overkill for my needs since I just need it one-way but I got tired of searching through a bajillion different parts.

I'll post an update once I get the parts and test them out. Can't wait!

[geoff body]

Anthony you could use the SN74LVC244A in that case

[Anthony Ortiz]

I received my SN74LVC245AN and was hooking it up for 3.3v -> 5v translation but As I read the data sheet I'm starting to think I made a mistake... although the specs state that it accepts input and supply voltages up to 6.5, the feature section states that it down-converts from 5 or 3.3 to 1.8, not vice versa. I'm guessing I read it wrong, that I can't feed an input at 3.3v and supply at 5v and expect it to work?

[Anthony Ortiz]

Okay, so I'm using an SN74LVC245A Octal Bus Transceiver to level-translate and buffer my Apple IIgs 1mhz (Phase 0) timer signal from 5v down to 3.3v and I am seeing some noise (or whatever it is) when reading the signal. Here is a pic of the source clock (top) and the level-translated 3.3v output of the same clock (bottom) : https://drive.google.com/file/d/0B-ZQ2AnS2r_6RlNrTW1tTDhvODhEZTdwUExXS2hDSEQ0aU1Z/view?usp=sharing

I see over/under shoot, don't know if that's normal, but the high-level of the 3.3v signal has less overshoot but more wavy than the low level; definitely not symmetrical! When polling the translated 3.3 clock signal on my Pi in a tight loop I get the data seen at the end of this post.

Any ideas?

[0 is LO, 1 is HI] followed by number of sequential occurrences

0 = 14076,1 = 34867,0 = 1,1 = 11,0 = 1,1 = 3,0 = 3,1 = 2,0 = 1,1 = 3,0 = 1,1 = 2,0 = 2,1 = 2,0 = 6,1 = 2,0 = 6,1 = 2,0 = 2,1 = 3,0 = 5,1 = 2,0 = 2,1 = 2,0 = 2,1 = 1,0 = 1,1 = 1,0 = 5,1 = 1,0 = 9,1 = 1,0 = 31670,1 = 34797,0 = 1,1 = 11,0 = 1,1 = 42,0 = 1,1 = 3,0 = 3,1 = 2,0 = 1,1 = 3,0 = 1,1 = 2,0 = 3,1 = 1,0 = 7,1 = 1,0 = 3,1 = 2,0 = 29631,1 = 34870,0 = 1,1 = 11,0 = 1,1 = 11,0 = 2,1 = 2,0 = 2,1 = 29,0 = 1,1 = 3,0 = 1,1 = 7,0 = 1,1 = 3,0 = 2,1 = 3,0 = 1,1 = 1,0 = 3,1 = 1,0 = 31725,1 = 34871,0 = 1,1 = 3,0 = 1,1 = 7,0 = 1,1 = 3,0 = 1,1 = 2,0 = 1,1 = 3,0 = 1,1 = 1,0 = 1,1 = 1,0 = 1,1 = 11,0 = 1,1 = 4,0 = 1,1 = 3,0 = 1,1 = 2,0 = 2,1 = 3,0 = 1,1 = 1,0 = 3,1 = 2,0 = 31674,1 = 32819,0 = 1,1 = 55,0 = 1,1 = 2,0 = 1,1 = 3,0 = 3,1 = 2,0 = 1,1 = 1,0 = 3,1 = 2,0 = 1,1 = 1,0 = 1,1 = 1,0 = 1,1 = 2,0 = 3,1 = 1,0 = 3,1 = 2,0 = 5,1 = 1,0 = 31686,1 = 34733,0 = 1,1 = 49,0 = 1,1 = 8,0 = 1,1 = 2,0 = 1,1 = 1,0 = 3,1 = 2,0 = 3,1 = 1,0 = 8,1 = 1,0 = 31688,1 = 34876,0 = 1,1 = 1,0 = 1,1 = 9,0 = 1,1 = 3,0 = 1,1 = 4,0 = 1,1 = 3,0 = 1,1 = 2,0 = 2,1 = 2,0 = 1,1 = 4,0 = 1,1 = 7,0 = 1,1 = 3,0 = 1,1 = 2,0 = 1,1 = 4,0 = 1,1 = 2,0 = 1,1 = 2,0 = 1,1 = 1,0 = 1,1 = 2,0 = 1,1 = 1,0 = 1,1 = 1,0 = 1,1 = 1,0 = 3,1 = 1,0 = 31692,1 = 32839,0 = 1,1 = 52,0 = 3,1 = 2,0 = 7,1 = 1,0 = 31691,1 = 34818,0 = 1,1 = 11,0 = 1,1 = 42,0 = 3,1 = 1,0 = 8,1 = 1,0 = 1,1 = 1,0 = 1,1 = 1,0 = 1,1 = 1,0 = 31720,1 = 32839,0 = 1,1 = 40,0 = 1,1 = 2,0 = 2,1 = 1,0 = 3,1 = 2,0 = 31699,1 = 34860,0 = 1,1 = 18,0 = 1,1 = 7,0 = 2,1 = 2,0 = 2,1 = 2,0 = 2,1 = 2,0 = 4,1 = 3,0 = 3,1 = 2,0 = 3,1 = 1,0 = 1,1 = 2,0 = 20,1 = 1,0 = 1,1 = 1,0 = 31670,1 = 34767,0 = 1,1 = 3,0 = 1,1 = 2,0 = 2,1 = 5,0 = 2,1 = 2,0 = 7,1 = 2,0 = 1,1 = 2,0 = 1,1 = 3,0 = 2,1 = 3,0 = 1,1 = 3,0 = 1,1 = 2,0 = 2,1 = 2,0 = 2,1 = 1,0 = 3,1 = 1,0 = 4,1 = 1,0 = 31673,1 = 32906,0 = 1,1 = 6,0 = 2,1 = 6,0 = 2,1 = 2,0 = 33,1 = 1,0 = 31608,1 = 34914,0 = 1,1 = 12,0 = 1,1 = 6,0 = 2,1 = 2,0 = 6,1 = 1,0 = 26,1 = 1,0 = 17,1 = 1,0 = 31721,1 = 32810,0 = 2,1 = 3,0 = 1,1 = 1,0 = 3,1 = 5,0 = 3,1 = 1,0 = 7,1 = 2,0 = 1,1 = 1,0 = 3,1 = 2,0 = 3,1 = 1,0 = 2,1 = 1,0 = 1,1 = 1,0 = 1,1 = 2,0 = 2,1 = 2,0 = 2,1 = 6,0 = 31696,1 = 34814,0 = 1,1 = 2,0 = 1,1 = 3,0 = 1,1 = 3,0 = 2,1 = 5,0 = 3,1 = 1,0 = 3,1 = 2,0 = 1,1 = 6,0 = 2,1 = 2,0 = 3,1 = 2,0 = 1,1 = 3,0 = 1,1 = 2,0 = 3,1 = 1,0 = 2,1 = 1,0 = 31632,1 = 34870,0 = 1,1 = 3,0 = 1,1 = 51,0 = 2,1 = 1,0 = 3,1 = 1,0 = 2,1 = 3,0 = 1,1 = 1,0 = 29726,1 = 34810,0 = 3,1 = 1,0 = 1,1 = 1,0 = 1,1 = 1,0 = 2,1 = 3,0 = 1,1 = 2,0 = 2,1 = 2,0 = 3,1 = 1,0 = 3,1 = 2,0 = 11,1 = 1,0 = 1,1 = 1,0 = 3,1 = 1,0 = 9,1 = 1,0 = 3,1 = 1,0 = 1,1 = 1,0 = 31615,1 = 34848,0 = 1,1 = 27,0 = 1,1 = 7,0 = 2,1 = 5,0 = 1,1 = 3,0 = 3,1 = 6,0 = 1,1 = 2,0 = 2,1 = 2,0 = 31747,1 = 32873,0 = 1,1 = 7,0 = 1,1 = 3,0 = 2,1 = 1,0 = 3,1 = 2,0 = 21,1 = 1

[Jorge]

Post by Anthony Ortiz
When polling the translated 3.3 clock signal on my Pi in a tight loop I get the data seen at the end of this post.
Any ideas?

The signal is about right imo, that ringing is not too bad, find a better/closer/shorter path to GND in which to plug the scope's GND tip to be sure. IOW the signals only look perfectly square in the datasheets... :-)

WRT the big number(s) of sequential ocurrences (e.g. 0 = 31699,1 = 34860) that is also normal because the Pi is time slicing your polling routine. Also, at what frequency are you sampling the gpios? See this:

http://codeandlife.com/2012/07/03/benchmarking-raspberry-pi-gpio-speed/

To poll the gpio C is best. But even so it will be time sliced out every so often by the scheduler.

[Anthony Ortiz]

Post by Jorge

Post by Anthony Ortiz
When polling the translated 3.3 clock signal on my Pi in a tight loop I get the data seen at the end of this post.
Any ideas?

The signal is about right imo, that ringing is not too bad, find a better/closer/shorter path to GND in which to plug the scope's GND tip to be sure. IOW the signals only look perfectly square in the datasheets... :-)
http://codeandlife.com/2012/07/03/benchmarking-raspberry-pi-gpio-speed/
To poll the gpio C is best. But even so it will be time sliced out every so often by the scheduler.
--
Jorge

Pi 3 runs at 1.1ghz and i'm sampling in a tight loop. The big number of sequential occurrences are strange because 1) they are supposed to be about the same but there is a 10% difference and 2) what's with all the other random noise? it seems to only happen right after the 1-> 0 transition but never after the 0 -> 1 transition... for some reason 0 -> 1 is perfectly clean! Also, I don't know why I'm getting so many samples... the Pi 3 is 1.1ghz, which is only 1100 times the speed of the 1mhz clock, which means I should get at most 1100 samples, not 60k+! Strange...

[Anthony Ortiz]

Post by Jorge
http://codeandlife.com/2012/07/03/benchmarking-raspberry-pi-gpio-speed/
To poll the gpio C is best. But even so it will be time sliced out every so often by the scheduler.
--
Jorge

Yes I am aware of that benchmark, and I am able to achieve almost 60mhz output via direct access to the registers, which is what I'm doing on the input side as well. In my case there's no os or interrupts as I'm doing this bare metal.

[Jorge]

Post by Anthony Ortiz
I'm doing this bare metal.

Wow that's cool! Have you got it @github perhaps? Can I see it or is it private? Now I'm curious, what exactly are you trying to do, if I may ask?

Then I've got another, new theory: what you're seeing may be a pattern of interference, a sort of "moiré".

Another idea: the rpi is prone to overheating when run @full speed, perhaps it's overheating? But that should not be it because you are using just one core, are you?

I've got no more ideas, it's too late for that. Good night!

Cheers,

[Michael J. Mahon]

Post by Anthony Ortiz
Okay, so I'm using an SN74LVC245A Octal Bus Transceiver to
level-translate and buffer my Apple IIgs 1mhz (Phase 0) timer signal from
5v down to 3.3v and I am seeing some noise (or whatever it is) when
reading the signal. Here is a pic of the source clock (top) and the
https://drive.google.com/file/d/0B-ZQ2AnS2r_6RlNrTW1tTDhvODhEZTdwUExXS2hDSEQ0aU1Z/view?usp=sharing
I see over/under shoot, don't know if that's normal, but the high-level
of the 3.3v signal has less overshoot but more wavy than the low level;
definitely not symmetrical! When polling the translated 3.3 clock signal
on my Pi in a tight loop I get the data seen at the end of this post.
Any ideas?
[0 is LO, 1 is HI] followed by number of sequential occurrences
0 = 14076,1 = 34867,0 = 1,1 = 11,0 = 1,1 = 3,0 = 3,1 = 2,0 = 1,1 = 3,0 =
1,1 = 2,0 = 2,1 = 2,0 = 6,1 = 2,0 = 6,1 = 2,0 = 2,1 = 3,0 = 5,1 = 2,0 =
2,1 = 2,0 = 2,1 = 1,0 = 1,1 = 1,0 = 5,1 = 1,0 = 9,1 = 1,0 = 31670,1 =
34797,0 = 1,1 = 11,0 = 1,1 = 42,0 = 1,1 = 3,0 = 3,1 = 2,0 = 1,1 = 3,0 =
1,1 = 2,0 = 3,1 = 1,0 = 7,1 = 1,0 = 3,1 = 2,0 = 29631,1 = 34870,0 = 1,1 =
11,0 = 1,1 = 11,0 = 2,1 = 2,0 = 2,1 = 29,0 = 1,1 = 3,0 = 1,1 = 7,0 = 1,1
= 3,0 = 2,1 = 3,0 = 1,1 = 1,0 = 3,1 = 1,0 = 31725,1 = 34871,0 = 1,1 = 3,0
= 1,1 = 7,0 = 1,1 = 3,0 = 1,1 = 2,0 = 1,1 = 3,0 = 1,1 = 1,0 = 1,1 = 1,0 =
1,1 = 11,0 = 1,1 = 4,0 = 1,1 = 3,0 = 1,1 = 2,0 = 2,1 = 3,0 = 1,1 = 1,0 =
3,1 = 2,0 = 31674,1 = 32819,0 = 1,1 = 55,0 = 1,1 = 2,0 = 1,1 = 3,0 = 3,1
= 2,0 = 1,1 = 1,0 = 3,1 = 2,0 = 1,1 = 1,0 = 1,1 = 1,0 = 1,1 = 2,0 = 3,1 =
1,0 = 3,1 = 2,0 = 5,1 = 1,0 = 31686,1 = 34733,0 = 1,1 = 49,0 = 1,1 = 8,0
= 1,1 = 2,0 = 1,1 = 1,0 = 3,1 = 2,0 = 3,1 = 1,0 = 8,1 = 1,0 = 31688,1 =
34876,0 = 1,1 = 1,0 = 1,1 = 9,0 = 1,1 = 3,0 = 1,1 = 4,0 = 1,1 = 3,0 = 1,1
= 2,0 = 2,1 = 2,0 = 1,1 = 4,0 = 1,1 = 7,0 = 1,1 = 3,0 = 1,1 = 2,0 = 1,1 =
4,0 = 1,1 = 2,0 = 1,1 = 2,0 = 1,1 = 1,0 = 1,1 = 2,0 = 1,1 = 1,0 = 1,1 =
1,0 = 1,1 = 1,0 = 3,1 = 1,0 = 31692,1 = 32839,0 = 1,1 = 52,0 = 3,1 = 2,0
= 7,1 = 1,0 = 31691,1 = 34818,0 = 1,1 = 11,0 = 1,1 = 42,0 = 3,1 = 1,0 =
8,1 = 1,0 = 1,1 = 1,0 = 1,1 = 1,0 = 1,1 = 1,0 = 31720,1 = 32839,0 = 1,1 =
40,0 = 1,1 = 2,0 = 2,1 = 1,0 = 3,1 = 2,0 = 31699,1 = 34860,0 = 1,1 = 18,0
= 1,1 = 7,0 = 2,1 = 2,0 = 2,1 = 2,0 = 2,1 = 2,0 = 4,1 = 3,0 = 3,1 = 2,0 =
3,1 = 1,0 = 1,1 = 2,0 = 20,1 = 1,0 = 1,1 = 1,0 = 31670,1 = 34767,0 = 1,1
= 3,0 = 1,1 = 2,0 = 2,1 = 5,0 = 2,1 = 2,0 = 7,1 = 2,0 = 1,1 = 2,0 = 1,1 =
3,0 = 2,1 = 3,0 = 1,1 = 3,0 = 1,1 = 2,0 = 2,1 = 2,0 = 2,1 = 1,0 = 3,1 =
1,0 = 4,1 = 1,0 = 31673,1 = 32906,0 = 1,1 = 6,0 = 2,1 = 6,0 = 2,1 = 2,0 =
33,1 = 1,0 = 31608,1 = 34914,0 = 1,1 = 12,0 = 1,1 = 6,0 = 2,1 = 2,0 = 6,1
= 1,0 = 26,1 = 1,0 = 17,1 = 1,0 = 31721,1 = 32810,0 = 2,1 = 3,0 = 1,1 =
1,0 = 3,1 = 5,0 = 3,1 = 1,0 = 7,1 = 2,0 = 1,1 = 1,0 = 3,1 = 2,0 = 3,1 =
1,0 = 2,1 = 1,0 = 1,1 = 1,0 = 1,1 = 2,0 = 2,1 = 2,0 = 2,1 = 6,0 = 31696,1
= 34814,0 = 1,1 = 2,0 = 1,1 = 3,0 = 1,1 = 3,0 = 2,1 = 5,0 = 3,1 = 1,0 =
3,1 = 2,0 = 1,1 = 6,0 = 2,1 = 2,0 = 3,1 = 2,0 = 1,1 = 3,0 = 1,1 = 2,0 =
3,1 = 1,0 = 2,1 = 1,0 = 31632,1 = 34870,0 = 1,1 = 3,0 = 1,1 = 51,0 = 2,1
= 1,0 = 3,1 = 1,0 = 2,1 = 3,0 = 1,1 = 1,0 = 29726,1 = 34810,0 = 3,1 = 1,0
= 1,1 = 1,0 = 1,1 = 1,0 = 2,1 = 3,0 = 1,1 = 2,0 = 2,1 = 2,0 = 3,1 = 1,0 =
3,1 = 2,0 = 11,1 = 1,0 = 1,1 = 1,0 = 3,1 = 1,0 = 9,1 = 1,0 = 3,1 = 1,0 =
1,1 = 1,0 = 31615,1 = 34848,0 = 1,1 = 27,0 = 1,1 = 7,0 = 2,1 = 5,0 = 1,1
= 3,0 = 3,1 = 6,0 = 1,1 = 2,0 = 2,1 = 2,0 = 31747,1 = 32873,0 = 1,1 = 7,0
= 1,1 = 3,0 = 2,1 = 1,0 = 3,1 = 2,0 = 21,1 = 1

Looks like a lot of ringing.

Are you using a 10x probe? A 1x probe will produce this effect. Using a
10x probe greatly reduces the load on the circuit and also reduces the
effect of the probe and its cable.

This ringing is almost certainly the result of the probe and not the
circuit.

[Anthony Ortiz]

Post by Michael J. Mahon

Post by Anthony Ortiz
Okay, so I'm using an SN74LVC245A Octal Bus Transceiver to
level-translate and buffer my Apple IIgs 1mhz (Phase 0) timer signal from
5v down to 3.3v and I am seeing some noise (or whatever it is) when
reading the signal. Here is a pic of the source clock (top) and the
https://drive.google.com/file/d/0B-ZQ2AnS2r_6RlNrTW1tTDhvODhEZTdwUExXS2hDSEQ0aU1Z/view?usp=sharing
I see over/under shoot, don't know if that's normal, but the high-level
of the 3.3v signal has less overshoot but more wavy than the low level;
definitely not symmetrical! When polling the translated 3.3 clock signal
on my Pi in a tight loop I get the data seen at the end of this post.
Any ideas?
[0 is LO, 1 is HI] followed by number of sequential occurrences
0 = 14076,1 = 34867,0 = 1,1 = 11,0 = 1,1 = 3,0 = 3,1 = 2,0 = 1,1 = 3,0 =
1,1 = 2,0 = 2,1 = 2,0 = 6,1 = 2,0 = 6,1 = 2,0 = 2,1 = 3,0 = 5,1 = 2,0 =
2,1 = 2,0 = 2,1 = 1,0 = 1,1 = 1,0 = 5,1 = 1,0 = 9,1 = 1,0 = 31670,1 =
34797,0 = 1,1 = 11,0 = 1,1 = 42,0 = 1,1 = 3,0 = 3,1 = 2,0 = 1,1 = 3,0 =
1,1 = 2,0 = 3,1 = 1,0 = 7,1 = 1,0 = 3,1 = 2,0 = 29631,1 = 34870,0 = 1,1 =
11,0 = 1,1 = 11,0 = 2,1 = 2,0 = 2,1 = 29,0 = 1,1 = 3,0 = 1,1 = 7,0 = 1,1
= 3,0 = 2,1 = 3,0 = 1,1 = 1,0 = 3,1 = 1,0 = 31725,1 = 34871,0 = 1,1 = 3,0
= 1,1 = 7,0 = 1,1 = 3,0 = 1,1 = 2,0 = 1,1 = 3,0 = 1,1 = 1,0 = 1,1 = 1,0 =
1,1 = 11,0 = 1,1 = 4,0 = 1,1 = 3,0 = 1,1 = 2,0 = 2,1 = 3,0 = 1,1 = 1,0 =
3,1 = 2,0 = 31674,1 = 32819,0 = 1,1 = 55,0 = 1,1 = 2,0 = 1,1 = 3,0 = 3,1
= 2,0 = 1,1 = 1,0 = 3,1 = 2,0 = 1,1 = 1,0 = 1,1 = 1,0 = 1,1 = 2,0 = 3,1 =
1,0 = 3,1 = 2,0 = 5,1 = 1,0 = 31686,1 = 34733,0 = 1,1 = 49,0 = 1,1 = 8,0
= 1,1 = 2,0 = 1,1 = 1,0 = 3,1 = 2,0 = 3,1 = 1,0 = 8,1 = 1,0 = 31688,1 =
34876,0 = 1,1 = 1,0 = 1,1 = 9,0 = 1,1 = 3,0 = 1,1 = 4,0 = 1,1 = 3,0 = 1,1
= 2,0 = 2,1 = 2,0 = 1,1 = 4,0 = 1,1 = 7,0 = 1,1 = 3,0 = 1,1 = 2,0 = 1,1 =
4,0 = 1,1 = 2,0 = 1,1 = 2,0 = 1,1 = 1,0 = 1,1 = 2,0 = 1,1 = 1,0 = 1,1 =
1,0 = 1,1 = 1,0 = 3,1 = 1,0 = 31692,1 = 32839,0 = 1,1 = 52,0 = 3,1 = 2,0
= 7,1 = 1,0 = 31691,1 = 34818,0 = 1,1 = 11,0 = 1,1 = 42,0 = 3,1 = 1,0 =
8,1 = 1,0 = 1,1 = 1,0 = 1,1 = 1,0 = 1,1 = 1,0 = 31720,1 = 32839,0 = 1,1 =
40,0 = 1,1 = 2,0 = 2,1 = 1,0 = 3,1 = 2,0 = 31699,1 = 34860,0 = 1,1 = 18,0
= 1,1 = 7,0 = 2,1 = 2,0 = 2,1 = 2,0 = 2,1 = 2,0 = 4,1 = 3,0 = 3,1 = 2,0 =
3,1 = 1,0 = 1,1 = 2,0 = 20,1 = 1,0 = 1,1 = 1,0 = 31670,1 = 34767,0 = 1,1
= 3,0 = 1,1 = 2,0 = 2,1 = 5,0 = 2,1 = 2,0 = 7,1 = 2,0 = 1,1 = 2,0 = 1,1 =
3,0 = 2,1 = 3,0 = 1,1 = 3,0 = 1,1 = 2,0 = 2,1 = 2,0 = 2,1 = 1,0 = 3,1 =
1,0 = 4,1 = 1,0 = 31673,1 = 32906,0 = 1,1 = 6,0 = 2,1 = 6,0 = 2,1 = 2,0 =
33,1 = 1,0 = 31608,1 = 34914,0 = 1,1 = 12,0 = 1,1 = 6,0 = 2,1 = 2,0 = 6,1
= 1,0 = 26,1 = 1,0 = 17,1 = 1,0 = 31721,1 = 32810,0 = 2,1 = 3,0 = 1,1 =
1,0 = 3,1 = 5,0 = 3,1 = 1,0 = 7,1 = 2,0 = 1,1 = 1,0 = 3,1 = 2,0 = 3,1 =
1,0 = 2,1 = 1,0 = 1,1 = 1,0 = 1,1 = 2,0 = 2,1 = 2,0 = 2,1 = 6,0 = 31696,1
= 34814,0 = 1,1 = 2,0 = 1,1 = 3,0 = 1,1 = 3,0 = 2,1 = 5,0 = 3,1 = 1,0 =
3,1 = 2,0 = 1,1 = 6,0 = 2,1 = 2,0 = 3,1 = 2,0 = 1,1 = 3,0 = 1,1 = 2,0 =
3,1 = 1,0 = 2,1 = 1,0 = 31632,1 = 34870,0 = 1,1 = 3,0 = 1,1 = 51,0 = 2,1
= 1,0 = 3,1 = 1,0 = 2,1 = 3,0 = 1,1 = 1,0 = 29726,1 = 34810,0 = 3,1 = 1,0
= 1,1 = 1,0 = 1,1 = 1,0 = 2,1 = 3,0 = 1,1 = 2,0 = 2,1 = 2,0 = 3,1 = 1,0 =
3,1 = 2,0 = 11,1 = 1,0 = 1,1 = 1,0 = 3,1 = 1,0 = 9,1 = 1,0 = 3,1 = 1,0 =
1,1 = 1,0 = 31615,1 = 34848,0 = 1,1 = 27,0 = 1,1 = 7,0 = 2,1 = 5,0 = 1,1
= 3,0 = 3,1 = 6,0 = 1,1 = 2,0 = 2,1 = 2,0 = 31747,1 = 32873,0 = 1,1 = 7,0
= 1,1 = 3,0 = 2,1 = 1,0 = 3,1 = 2,0 = 21,1 = 1

Looks like a lot of ringing.
Are you using a 10x probe? A 1x probe will produce this effect. Using a
10x probe greatly reduces the load on the circuit and also reduces the
effect of the probe and its cable.
This ringing is almost certainly the result of the probe and not the
circuit.
--
-michael - NadaNet 3.1 and AppleCrate II: http://michaeljmahon.com

Wow! I just checked the probes and indeed they are set to 1x. I'll set them to 10x and see what happens. I'm just using an oscilloscope for the first time so I'm very new to this and only know the really basic stuff. Will post my results soon!

[Anthony Ortiz]

Post by Anthony Ortiz

Post by Michael J. Mahon

Post by Anthony Ortiz
Okay, so I'm using an SN74LVC245A Octal Bus Transceiver to
level-translate and buffer my Apple IIgs 1mhz (Phase 0) timer signal from
5v down to 3.3v and I am seeing some noise (or whatever it is) when
reading the signal. Here is a pic of the source clock (top) and the
https://drive.google.com/file/d/0B-ZQ2AnS2r_6RlNrTW1tTDhvODhEZTdwUExXS2hDSEQ0aU1Z/view?usp=sharing
I see over/under shoot, don't know if that's normal, but the high-level
of the 3.3v signal has less overshoot but more wavy than the low level;
definitely not symmetrical! When polling the translated 3.3 clock signal
on my Pi in a tight loop I get the data seen at the end of this post.
Any ideas?
[0 is LO, 1 is HI] followed by number of sequential occurrences
0 = 14076,1 = 34867,0 = 1,1 = 11,0 = 1,1 = 3,0 = 3,1 = 2,0 = 1,1 = 3,0 =
1,1 = 2,0 = 2,1 = 2,0 = 6,1 = 2,0 = 6,1 = 2,0 = 2,1 = 3,0 = 5,1 = 2,0 =
2,1 = 2,0 = 2,1 = 1,0 = 1,1 = 1,0 = 5,1 = 1,0 = 9,1 = 1,0 = 31670,1 =
34797,0 = 1,1 = 11,0 = 1,1 = 42,0 = 1,1 = 3,0 = 3,1 = 2,0 = 1,1 = 3,0 =
1,1 = 2,0 = 3,1 = 1,0 = 7,1 = 1,0 = 3,1 = 2,0 = 29631,1 = 34870,0 = 1,1 =
11,0 = 1,1 = 11,0 = 2,1 = 2,0 = 2,1 = 29,0 = 1,1 = 3,0 = 1,1 = 7,0 = 1,1
= 3,0 = 2,1 = 3,0 = 1,1 = 1,0 = 3,1 = 1,0 = 31725,1 = 34871,0 = 1,1 = 3,0
= 1,1 = 7,0 = 1,1 = 3,0 = 1,1 = 2,0 = 1,1 = 3,0 = 1,1 = 1,0 = 1,1 = 1,0 =
1,1 = 11,0 = 1,1 = 4,0 = 1,1 = 3,0 = 1,1 = 2,0 = 2,1 = 3,0 = 1,1 = 1,0 =
3,1 = 2,0 = 31674,1 = 32819,0 = 1,1 = 55,0 = 1,1 = 2,0 = 1,1 = 3,0 = 3,1
= 2,0 = 1,1 = 1,0 = 3,1 = 2,0 = 1,1 = 1,0 = 1,1 = 1,0 = 1,1 = 2,0 = 3,1 =
1,0 = 3,1 = 2,0 = 5,1 = 1,0 = 31686,1 = 34733,0 = 1,1 = 49,0 = 1,1 = 8,0
= 1,1 = 2,0 = 1,1 = 1,0 = 3,1 = 2,0 = 3,1 = 1,0 = 8,1 = 1,0 = 31688,1 =
34876,0 = 1,1 = 1,0 = 1,1 = 9,0 = 1,1 = 3,0 = 1,1 = 4,0 = 1,1 = 3,0 = 1,1
= 2,0 = 2,1 = 2,0 = 1,1 = 4,0 = 1,1 = 7,0 = 1,1 = 3,0 = 1,1 = 2,0 = 1,1 =
4,0 = 1,1 = 2,0 = 1,1 = 2,0 = 1,1 = 1,0 = 1,1 = 2,0 = 1,1 = 1,0 = 1,1 =
1,0 = 1,1 = 1,0 = 3,1 = 1,0 = 31692,1 = 32839,0 = 1,1 = 52,0 = 3,1 = 2,0
= 7,1 = 1,0 = 31691,1 = 34818,0 = 1,1 = 11,0 = 1,1 = 42,0 = 3,1 = 1,0 =
8,1 = 1,0 = 1,1 = 1,0 = 1,1 = 1,0 = 1,1 = 1,0 = 31720,1 = 32839,0 = 1,1 =
40,0 = 1,1 = 2,0 = 2,1 = 1,0 = 3,1 = 2,0 = 31699,1 = 34860,0 = 1,1 = 18,0
= 1,1 = 7,0 = 2,1 = 2,0 = 2,1 = 2,0 = 2,1 = 2,0 = 4,1 = 3,0 = 3,1 = 2,0 =
3,1 = 1,0 = 1,1 = 2,0 = 20,1 = 1,0 = 1,1 = 1,0 = 31670,1 = 34767,0 = 1,1
= 3,0 = 1,1 = 2,0 = 2,1 = 5,0 = 2,1 = 2,0 = 7,1 = 2,0 = 1,1 = 2,0 = 1,1 =
3,0 = 2,1 = 3,0 = 1,1 = 3,0 = 1,1 = 2,0 = 2,1 = 2,0 = 2,1 = 1,0 = 3,1 =
1,0 = 4,1 = 1,0 = 31673,1 = 32906,0 = 1,1 = 6,0 = 2,1 = 6,0 = 2,1 = 2,0 =
33,1 = 1,0 = 31608,1 = 34914,0 = 1,1 = 12,0 = 1,1 = 6,0 = 2,1 = 2,0 = 6,1
= 1,0 = 26,1 = 1,0 = 17,1 = 1,0 = 31721,1 = 32810,0 = 2,1 = 3,0 = 1,1 =
1,0 = 3,1 = 5,0 = 3,1 = 1,0 = 7,1 = 2,0 = 1,1 = 1,0 = 3,1 = 2,0 = 3,1 =
1,0 = 2,1 = 1,0 = 1,1 = 1,0 = 1,1 = 2,0 = 2,1 = 2,0 = 2,1 = 6,0 = 31696,1
= 34814,0 = 1,1 = 2,0 = 1,1 = 3,0 = 1,1 = 3,0 = 2,1 = 5,0 = 3,1 = 1,0 =
3,1 = 2,0 = 1,1 = 6,0 = 2,1 = 2,0 = 3,1 = 2,0 = 1,1 = 3,0 = 1,1 = 2,0 =
3,1 = 1,0 = 2,1 = 1,0 = 31632,1 = 34870,0 = 1,1 = 3,0 = 1,1 = 51,0 = 2,1
= 1,0 = 3,1 = 1,0 = 2,1 = 3,0 = 1,1 = 1,0 = 29726,1 = 34810,0 = 3,1 = 1,0
= 1,1 = 1,0 = 1,1 = 1,0 = 2,1 = 3,0 = 1,1 = 2,0 = 2,1 = 2,0 = 3,1 = 1,0 =
3,1 = 2,0 = 11,1 = 1,0 = 1,1 = 1,0 = 3,1 = 1,0 = 9,1 = 1,0 = 3,1 = 1,0 =
1,1 = 1,0 = 31615,1 = 34848,0 = 1,1 = 27,0 = 1,1 = 7,0 = 2,1 = 5,0 = 1,1
= 3,0 = 3,1 = 6,0 = 1,1 = 2,0 = 2,1 = 2,0 = 31747,1 = 32873,0 = 1,1 = 7,0
= 1,1 = 3,0 = 2,1 = 1,0 = 3,1 = 2,0 = 21,1 = 1

Looks like a lot of ringing.
Are you using a 10x probe? A 1x probe will produce this effect. Using a
10x probe greatly reduces the load on the circuit and also reduces the
effect of the probe and its cable.
This ringing is almost certainly the result of the probe and not the
circuit.
--
-michael - NadaNet 3.1 and AppleCrate II: http://michaeljmahon.com

Wow! I just checked the probes and indeed they are set to 1x. I'll set them to 10x and see what happens. I'm just using an oscilloscope for the first time so I'm very new to this and only know the really basic stuff. Will post my results soon!

I tried setting probes to 10x but it squashed the original 5v clock signal and flatlined into a faint blinking horizontal line on the 3.3v level-translated clock signal.

[Jorge]

Post by Anthony Ortiz
I tried setting probes to 10x but it squashed the original 5v clock signal and flatlined into a faint blinking horizontal line on the 3.3v level-translated clock signal.

That was to be expected. You've got to poke 10x in the scope settings for that probe/channel.

[Michael J. Mahon]

Post by Jorge

Post by Anthony Ortiz
I tried setting probes to 10x but it squashed the original 5v clock
signal and flatlined into a faint blinking horizontal line on the 3.3v
level-translated clock signal.

That was to be expected. You've got to poke 10x in the scope settings for
that probe/channel.

Right!

The 10x probe reduces resistive and capacitive loading by a factor of ten,
and it does that by attenuating the signal by a factor of ten.

That should not be a problem with logic-level signals, since the
oscilloscope has plenty of vertical gain to spare.

[cb meeks]

Post by Anthony Ortiz
I'm looking to have my Raspberry Pi communicate with the Apple IIe via a peripheral slot and have decided that the "bus" I'm going to use to interface them both is the 574. I have some 374's in front of me but I much prefer the pin arrangement on the 574. My question is, should I use the CMOS or TTL logic level version? Also, what level converter would you guys recommend for 3.3 -> 5 and vice-versa?

WAIT...you said LATCH.

Sorry...never mind. I didn't read that closely.

[Anthony Ortiz]

My transceiver datasheet is recommending a bypass capacitor for its 5v Vcc, which I'm sourcing from the 5v line on the Apple II bus. Any recommendations on parallel resistor/capacitor combo?

[Anthony Ortiz]

Post by Anthony Ortiz
My transceiver datasheet is recommending a bypass capacitor for its 5v Vcc, which I'm sourcing from the 5v line on the Apple II bus. Any recommendations on parallel resistor/capacitor combo?

Sorry, forgot the other supply (it's dual supply)... one side sources 5v from Apple II, the other side sources 3.3v from Pi. I need bypass capacitors for both sides and could use some recommendations.

[Michael J. Mahon]

Post by Anthony Ortiz

Post by Anthony Ortiz
My transceiver datasheet is recommending a bypass capacitor for its 5v
Vcc, which I'm sourcing from the 5v line on the Apple II bus. Any
recommendations on parallel resistor/capacitor combo?

Sorry, forgot the other supply (it's dual supply)... one side sources 5v
from Apple II, the other side sources 3.3v from Pi. I need bypass
capacitors for both sides and could use some recommendations.

Standard bypassing for drivers is 0.1uF from each supply to ground, as
close to the chip's power pins as possible.

[Anthony Ortiz]

Thanks Michael. Couple of related questions :

1) online I see mention of a parallel resistor; any particular one I should be using?

2) any particular type of capacitor (e.g. Ceramic?)

3) if I need to drive several transceivers, do I need a bypass capacitor for each one or can I drive them from a single one?

Thanks!

Anthony

[Michael J. Mahon]

Post by Anthony Ortiz
1) online I see mention of a parallel resistor; any particular one I should be using?

In parallel with what? Is this a bus terminator (one resistor per output)?
That would be unnecessary for a short bus.

Post by Anthony Ortiz
2) any particular type of capacitor (e.g. Ceramic?)

Yes, typically ceramic/monolithic. All printed circuit boards are covered
with them!

Post by Anthony Ortiz
3) if I need to drive several transceivers, do I need a bypass capacitor
for each one or can I drive them from a single one?

Each chip should have a bypass cap.

Post by Anthony Ortiz
Thanks!

Glad to help--sounds like fun!

[Anthony Ortiz]

Thanks to everyone for all the assistance. Tonight I finally managed to interface my Pi with the Apple II bus at 1mhz and via GPIO read the three bytes from ROM at $FDED. Next is some writes, but tonight I sleep the sleep of babes...

[Anthony Ortiz]

I need to add a delay to one of my 5v control lines; any recommendations? I see the SN74LS31 and like the different delays but the inverting and nand ports are waste of space for me. This place has a nice selection but can't find their chips sold anywhere : http://www.datadelay.com/asp/monolith.asp.

[Michael J. Mahon]

Post by Anthony Ortiz
I need to add a delay to one of my 5v control lines; any recommendations?
I see the SN74LS31 and like the different delays but the inverting and
nand ports are waste of space for me. This place has a nice selection but
can't find their chips sold anywhere : http://www.datadelay.com/asp/monolith.asp.

It's actually quite common to use an RC network for small delays. (Clocking
a 6522 from phi2 is a typical example).