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I have good news, but also something weird that probably has a simpler solution. First, after reversing the bit order for LSB/MSB, the data is just the lower 128 characters of ASCII. Nothing fancy. Just mask out the top bit (end of string bit) and print the character. You don't need special...

Very cool detective work. However, I don't quite understand the bit pattern. In your post, you say the char data offset is bits 1-4. That only allows for 16 characters. in your code, you seem to be using bits 1-5 (aka 0-4) which would provide 32 characters (minus 1 for the special case space)...

I have a number of Quadra 630 computers. Recently, I picked up a spare board that motivated me to take a closer look at some of the differences. Thus far, I have found three different boards in Quadra/LC 630 series of computers: 820-0548-B (the most common). One double-bank RAM slot. One...

Yes! It is my hope that people will replicate as much of the software, manuals, and knowledge into as many public repositories as possible. I think we all recognize that any single site can disappear from the internet without warning. I am glad to be part of a community that recognizes the value...

Good advice and video. This year, I wrote an application that combines the BinHex (.hqx) file converter and communication software. It works on all Macintosh computers from System 1 to System 9, including emulators. And, like in the video, you can use any terminal application on a PC or modern...

That's incredible! Good write up. Thank you for sharing this.

Just to be clear, the modem port will work fine. That resistor is part of the board as shipped by Apple. So, don't remove it.

That is R8 100K which pulls RXD+ high (to 5V) on the modem port. This would provide a default signal to prevent electrical noise from being interpreted as incoming data. The modem port is serviced by an interrupt (unlike the printer port in early Macs), and thus false incoming data could...

I'm surprised (pleasantly) that it works in OS 9. BTW, I noticed that async calls to the serial driver cause Basilisk II to stutter.

Inside Macintosh claims the SCSI manager is not capable of asynchronous operation. Furthermore, any call that requires a memory allocation also does not work asynchronously. When you pre-read the file using Resourcerer, it is likely fitting into the cache. This would avoid calls to the SCSI...

Yes, I strongly considered it. Zmodem definitely has higher performance than Xmodem, as well as the ability to continue an interrupted file transfer from where it left off. The power of Zmodem is that it uses a file offset rather than arbitrary packet numbers with ack/nak. That way you can tell...

Hello everyone, For bulk file copying on older Macs, nothing beats emulated hardware such as Floppy Emu, MacSD, ZuluSCSI, and so on. However, for sending small files back and forth, swapping the micro SD card in and out can feel a bit like sneakernet. I've written a small application that runs...

Awesome! That is so much better. I have no doubt that if we can hear the difference (we can) then we can measure the difference. Here are the other steps from my earlier post. Basically, the methodology is to find pairs of test points up and down the sound chain. Hopefully, by comparing the...

I've figured it out. It's the vertical scale you've set both your probes to. Try 1V or maybe even 500 mV per division.

Good video. Don't give up. Something is just not right about the noise floor on your oscilloscope. There is no way there is basically a 1V difference between your two probes. Could you email Rigol support and ask what the expected level should be for your scope in A-B math mode? I think we need...

Although the setup looks correct, the 800 mV noise floor is freaking me out. It should be an order of magnitude lower. Am I being tricked by the 10x probe? In any case, you definitely see the difference in the final two images from the scope. Even if the scale is off or the base noise is higher...

I have edited my prior message to now say 'math-subtract' mode to avoid confusion for future readers. Originally, I used the word 'differential' which may not be the right terminology.

Your Rigol scope is perfect for this test. For this, we care about the scope feature, not the probes. I assume both of your probes are in 10:1 configuration? Put the CH1 probe on U15B pin 12. Put the CH2 probe on U15C pin 12. I guess connect the ground of both probes together. Funny, I haven't...

I suspect the LCD electrical noise is being injected (or not filtered) in the above area of the circuit. Here's what I would check: 1. Obviously look carefully for loose pins or corrosion in this area. I suspect you've already done this. Any resistance on the ground or power supply connections...

My hope is that if you can reproduce this on demand by varying the pixels on the display, it: 1. May help you follow the noise through the circuit. 2. May suggest a problem with the LCD grounding/filtering 3. May suggest there is a grounding or filtering issue on the sound circuit, as opposed to...