Cassette motor control question

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Mike Ladwig

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May 27, 2022, 6:46:01 PMMay 27
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Hi!

I'm working on finishing my Arduino -based cassette drive, finally completed the record functionality only to find out that my record motor control doesn't seem to be working. I've traced the H8-5 'motor on' control circuitry back to the USART and I don't ever see TXE go low when I start to record. So, I'm wondering if I'm doing something wrong with PAM.

As I understand it, I should be able to load a binary program and after it finishes loading, press the 'Dump' button and have it kick off the recording process. Is this correct, or am I missing something?

Thanks!

norberto.collado koyado.com

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May 27, 2022, 7:58:55 PMMay 27
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I have sane issue on my new H8-Z5-4 board. With Terry S. help, we found that only the INS8251 works to do this. If you do not have such IC, it doesn't work.

This is the behavior: 

INS8251 - When data is in the transmit buffer it will drive TXE low, which will turn on the motor, and drive /CTS low (5 sec timer).
Any other 8251/82C51 vendor - When data is in the transmit buffer it will "NOT" drive TXE low, unless /CTS is low first. So, the cassette motor will never turn on as /CTS is high waiting for TXE to bring it low. I tested Intel 8251 and other with same issue. I ordered some INS8251 and waiting for them to test them out. 

Can you verify which 8251 type you have?

We are still brainstorming on how to fix this with hardware. 🙁

Thanks,
Norberto


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Subject: [sebhc] Cassette motor control question
 
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Mike Ladwig

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May 27, 2022, 8:19:14 PMMay 27
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Wow interesting! Lucky for me you were "first over the hill" on this issue -- I would have pulled out all of my hair before even thinking of this cause.

It looks as if I have two different 8251s: one from NEC (IC123) and one from Intel (IC124).

norberto.collado koyado.com

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May 27, 2022, 8:25:08 PMMay 27
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You can only do the "Load" function with those 8251's, but not the "Dump" function. Once I get the INS8251, I will test one and send it to you.

Norby

Sent: Friday, May 27, 2022 5:19 PM
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Subject: Re: [sebhc] Cassette motor control question
 

Mike Ladwig

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Jun 2, 2022, 6:43:47 PMJun 2
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Just to close this out, I realized today that I had a couple of INS8251 in my spares and swapped one in. Worked like a charm and now I have record motor control functionality.

When reading up on this issue, I found a reference to Intel licensing the chip implementation to NEC (and perhaps others) but that many clones (like INS probably) were implementations from the data sheet. I also found a few notes about people having to work around other implementation errata with this generation of USARTS.

Mike Ladwig

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Jun 2, 2022, 7:11:53 PMJun 2
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Of course, it wouldn't be a step forward without also taking a step back. Apparently my five second delay circuit doesn't work as a dump doesn't get any lead-in. Back to tracing signals on my oscilloscope...

Douglas Miller

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Jun 2, 2022, 7:14:09 PMJun 2
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Just to be clear, INS is National Semiconductor a.k.a. "NS". I don't recall NEC (Nippon Electric Corp) being a big player in the U.S in the late 70's, but maybe they were. I would expect that NS could easily have been an official second-source (often a requirement for Military/Government contracts), and thus the chip was likely identical to Intel's. Conjecture, of course.

Mike Ladwig

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12:08 PM (11 hours ago) 12:08 PM
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An update: my missing five second lead-in delay on record was caused by a bad 33uF tantalum (C111 I think). If anyone has the same issue, I'd be happy to send you a capacitor from the small pouch of them I now have.

norberto.collado koyado.com

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2:01 PM (9 hours ago) 2:01 PM
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Glad to know that your board is up and running. I did receive the INS8251 and will test them during the weekend. 

I'm going to delete the current HA-Z5-4 board design as it only works with the H89 tapes and not with the H8 tapes. I will start a new board duplicating the H8-5 original design. 

Norberto

Sent: Friday, June 24, 2022 9:08 AM
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