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BigDumbDinosaur
 Post subject: NXP 28L92 DUAL UART
PostPosted: Thu Aug 11, 2022 6:05 am 
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NXP DUAL UART DISCONTINUED

This post is to inform everyone who uses the NXP 28L92 dual UART (DUART) that NXP has discontinued its production and what inventory was present at major vendors such as Digi-Key and Mouser is gone. I spoke with someone at NXP’s US sales office and was told that NXP has stopped producing their entire industrial UART line, of which the 28L92 is part. The reason given was the primary usage of these parts, automotive data buses, has dried up, with integrated CAN bus controllers taking over.

Fortunately, there are alternatives. MaxLinear’s Exar XR88C192 is hardware- and software-compatible with the 28L92 when the latter is operating in x86 mode, which is what I recommend for use in our systems (if you prefer operating in Motorola mode, there is the XR68C192). The fly in the ointment is the XR88C192 and XR68C192 are only available in a 44-pin LQFP package with 0.8mm pin pitch. MaxLinear indicates these parts will be in production for the foreseeable future.

Another alternative is to use Exar’s XR88C92, which is available in PLCC44 (e.g., Digi-Key has them). The XR88C92 is functionally identical to NXP’s 26C92 DUART, which is the DUART I ran in POC V1.1 before switching to the 28L92. The XR88C92 is plug-compatible with either NXP product and excepting its smaller 8-byte receive and transmit FIFO sizes, is software-compatible with both the XR88C192 and 28L92. Hence the XR88C92 can be considered a drop-in substitute for the 28L92 with only a trivial change to the device's configuration. In most applications, the smaller FIFOs won’t be of any significant consequence in systems that take advantage of the FIFOs—an increase in IRQs during sustained communication will be the primary difference.

Something that is under consideration is offering a “kit” to anyone who would like to use the XR88C192 in new designs but is put off by the prospect of having to handle and solder an LQFP package. Whether such a kit will materialize will depend on if there is enough expressed interest.

Attachment:
File comment: Exar XR88C92/XR88C192 Data Sheet
duart_88c92_88c192.pdf [1.82 MiB]
Downloaded 93 times
Attachment:
File comment: XR88C192 vs. 28L92 Compatability White Paper
28l92_compatibility.pdf [32.3 KiB]
Downloaded 89 times

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akohlbecker
 Post subject: Re: NXP 28L92 DUAL UART
PostPosted: Thu Aug 11, 2022 10:26 am 
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Did you ever consider using TI's TL16C550 line? Or TL16C552 for dual channel? They both have plenty of stock, and at first glance seem like functionally equivalent

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floobydust
 Post subject: Re: NXP 28L92 DUAL UART
PostPosted: Thu Aug 11, 2022 1:17 pm 
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Well, that wasn't very nice of NXP....

In addition to the Exar (now MaxLinear), TI also has their version of the 29L92 DUART, the TL28L92. Currently no stock at Mouser but shows a quantity on order.

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BigDumbDinosaur
 Post subject: Re: NXP 28L92 DUAL UART
PostPosted: Thu Aug 11, 2022 8:48 pm 
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akohlbecker wrote:
Did you ever consider using TI's TL16C550 line? Or TL16C552 for dual channel? They both have plenty of stock, and at first glance seem like functionally equivalent

The 16C55x series does not have the precision 16-bit counter/timer (C/T) that the NXP and Exar products have. The C/T is independent of the bit rate generator that regulates serialization/deserialization, making the C/T useful for generating a stable jiffy IRQ. I and others who use the 28L92 exploit this feature for timekeeping purposes, e.g., system uptime, time-of-day, etc. Also, the Exar and NXP UARTs have a multitude of multipurpose inputs and outputs that are quite useful for out-of-band signalling and control purposes. These are not present in the 16C55x series.

Software-wise, there is no commonality between the NXP 28L92 and the 16C552. Register assignments and functions are completely different, and the procedures for setting up bit rates, data formats, interrupt sources, etc., are completely different. A total driver rewrite would be required.

The 16C550 itself has a chip design defect that makes use of the receiver FIFO essentially impossible. It should not be used in any new design. Instead, the 16C550A should be used.

Incidentally, the 16C55x series of UARTs is produced by many manufacturers, Exar and NXP being among them. I believe the original producer of the 16C55x series was National Semiconductor back in the early 1990s when the weaknesses of the older Intel-compatible UARTs, especially the 8250 (also developed by National c. 1980), became painfully evident. TI became a producer of 16C55x (and later) UARTs when they bought out National in 2011.

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Last edited by BigDumbDinosaur on Fri Aug 12, 2022 2:33 am, edited 1 time in total.

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BigDumbDinosaur
 Post subject: Re: NXP 28L92 DUAL UART
PostPosted: Thu Aug 11, 2022 9:19 pm 
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floobydust wrote:
Well, that wasn't very nice of NXP....

I think they kind of lost their way following their divestiture from Phillips in 2006. I've been using Phillips/NXP UARTs for 32 years, and have accumulated a lot of experience in designing them into things, as well as programming them. If that hadn't been the case and I had to rely on NXP technical support, I'd have given up on them long ago and found another way.

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In addition to the Exar (now MaxLinear), TI also has their version of the 29L92 DUART, the TL28L92. Currently no stock at Mouser but shows a quantity on order.

The TL28L92 is a QFP-44 package with 0.8mm pin pitch. The Exar 88C192 is an LQFP-44 with 0.8mm pin pitch. Based on that, and also that the Exar product is less expensive, I wouldn't bother with the TI part. Also, TI's lead time is over a year.

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akohlbecker
 Post subject: Re: NXP 28L92 DUAL UART
PostPosted: Fri Aug 12, 2022 9:52 am 
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Interesting insight, thanks BDD.

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floobydust
 Post subject: Re: NXP 28L92 DUAL UART
PostPosted: Fri Aug 12, 2022 8:58 pm 
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BDD,

Agreed on the Exar part... I picked up a couple of these years ago... I've just added the TI part for awareness... who knows, at some point the Exar part might disappear as well, so having an additional source can't hurt.

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BigDumbDinosaur
 Post subject: Re: NXP 28L92 DUAL UART
PostPosted: Sat Aug 13, 2022 1:34 am 
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floobydust wrote:
BDD,

Agreed on the Exar part... I picked up a couple of these years ago... I've just added the TI part for awareness... who knows, at some point the Exar part might disappear as well, so having an additional source can't hurt.

Yep! When company B acquires company A, one of the first things B will do is shed personnel, usually followed by products that are thought to be slow-sellers. I’ve seen it many times. TI, on the other hand, likes to expand their product line, so their rendition of the 28L92 could be around for many years.

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floobydust
 Post subject: Re: NXP 28L92 DUAL UART
PostPosted: Thu Aug 18, 2022 5:16 pm 
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Turns out Arrow has decent stock... for the moment at least:

https://www.arrow.com/en/products/sc28l ... conductors

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BigDumbDinosaur
 Post subject: Re: NXP 28L92 DUAL UART
PostPosted: Thu Aug 18, 2022 5:41 pm 
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floobydust wrote:
Turns out Arrow has decent stock... for the moment at least:

https://www.arrow.com/en/products/sc28l ... conductors

That one is the QFP package.

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floobydust
 Post subject: Re: NXP 28L92 DUAL UART
PostPosted: Thu Aug 18, 2022 6:07 pm 
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Yes, quad flat pack... which is what I'll be using going forward. With the exception of EEPROMs, I rarely remove a chip from a socket, perhaps a few times in the past 5 years. I'm slowly transitioning to all SMT parts, sans EEPROM/NOR Flash chips, which I'm moving to PLCC-32 versions. I have the PLCC adapter for the Dataman to program them, so that's my plan going forward.

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BigDumbDinosaur
PostPosted: Wed Sep 21, 2022 3:48 am 
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I'm giving this topic a bump, just in case someone missed it.

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Sheep64
 Post subject: Re: NXP 28L92 DUAL UART
PostPosted: Mon Nov 21, 2022 12:01 pm 
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BigDumbDinosaur: From your repeated advocacy of 28L92, I finally understand its merit. Serial plus parallel plus timers means that one 28L92 replaces one 6522 and two 6551 in applications where 6522 has surplus functionality or 6551 is too slow. Where a large number of parallel pins may be required, 28L92 may be extended with cheap shift registers. For example, it would be possible to make a serial terminal with 28L92 timers to blink cursor, 28L92 with shift registers to a keyboard matrix, UART (obviously), alternate UART and 6845 or similar for display. It is a shame that Intel/Motorola bus selectable versions aren't available. I presume that it is more profitable to omit the hair of gold wire required to bond one pin and instead segment the market with two incompatible derivatives.

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BigDumbDinosaur
 Post subject: Re: NXP 28L92 DUAL UART
PostPosted: Mon Nov 21, 2022 9:08 pm 
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Sheep64 wrote:
It is a shame that Intel/Motorola bus selectable versions aren't available.

I’ve never operated the NXP UARTs in Motorola bus mode, so omission of that feature is of no consequence to me.

There are potential timing “gotchas” with using a Motorola-style bus, especially with the 65C816. While the (default) Intel-style bus mode adds a little complication to the reset and read/write circuitry, it’s trivial. The payoff is the ability to precisely control when the UART is listening or talking on the data bus.

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BigDumbDinosaur
PostPosted: Thu Apr 06, 2023 9:35 pm 
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PRODUCT AVAILABILITY UPDATE

I was advised today by my sales rep at Mouser that they have received 2,000 pieces of 28L92 DUARTs in PLCC-44. This is NXP part number SC28L92A1A,518, which is what I am using in my POC units.

If you’ve been hankering to try out this device but were put off at the thought of dealing with the dinky QFP44 package, here’s your chance! I wouldn’t wait too long to act, as I suspect that inventory is going to go fairly quickly. The Exar and TI equivalents are also in stock, but are in QFP, not PLCC.

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