Forums

I2C master

Started by David Lesher September 22, 2017
On 26/09/17 07:59, whit3rd wrote:
> On Monday, September 25, 2017 at 12:56:18 AM UTC-7, David Brown wrote: >> On 23/09/17 04:42, Tim Williams wrote: >>> "rickman" <gnuarm@gmail.com> wrote in message >>> news:oq49e4$tqk$1@dont-email.me... >>>>> Thanks, we'll eschew. RS-232 may be old and slow but works.... > >>>> It's also not multi-master... I guess you can roll your own. >>> >>> RS-485 is a solved problem, cheap, and noise tolerant. Or CAN, if you >>> don't mind a little more hardware (often provided in MCUs) and more >>> automation as far as the bus dealing with bus-y problems all by itself. >>> >>> These might be a little hungry, or overly robust. If you need lower >>> current consumption, and the signal doesn't have to leave the board, an >>> open collector bus (like I2C) is still a good idea. >> >> Or you can use CAN controllers in microcontrollers, but with a simple >> open collector bus. You get the best of all worlds then > > Well, not ALL worlds. Ethernet has better distance, and RS-423 with > terminators (sold widely as LocalTalk by Apple, with third parties making > ports that work for Windows) does good fast serial with (nominally) > about 500m wire limits. > > Open collector is kinda... IEEE-488. Short distance and low bitrate. >
OK, not /all/ worlds. It only makes sense for local connections, such as between devices on a board or on closely-coupled boards. But the context was in comparison with I&sup2;C, and anywhere that I&sup2;C would work, CAN with an open collector bus would also work - just with much easier multi-mastering.
On Mon, 25 Sep 2017 22:59:43 -0700 (PDT), whit3rd <whit3rd@gmail.com>
wrote:

>On Monday, September 25, 2017 at 12:56:18 AM UTC-7, David Brown wrote: >> On 23/09/17 04:42, Tim Williams wrote: >> > "rickman" <gnuarm@gmail.com> wrote in message >> > news:oq49e4$tqk$1@dont-email.me... >> >>> Thanks, we'll eschew. RS-232 may be old and slow but works.... > >> >> It's also not multi-master... I guess you can roll your own. >> > >> > RS-485 is a solved problem, cheap, and noise tolerant. Or CAN, if you >> > don't mind a little more hardware (often provided in MCUs) and more >> > automation as far as the bus dealing with bus-y problems all by itself. >> > >> > These might be a little hungry, or overly robust. If you need lower >> > current consumption, and the signal doesn't have to leave the board, an >> > open collector bus (like I2C) is still a good idea. >> >> Or you can use CAN controllers in microcontrollers, but with a simple >> open collector bus. You get the best of all worlds then > >Well, not ALL worlds. >Ethernet has better distance,
10Base2/5 and 10BaseT with hubs had only CD (Collision Detect) arbitration. On 10/100/1000BaseT with some extra hardware (switches) is needed to queue the messages to other ports.
>and RS-423 with >terminators (sold widely as LocalTalk by Apple, with third parties making >ports that work for Windows) does good fast serial with (nominally) >about 500m wire limits.
Is that RS-423 (a.k.a DEC-423) shit still around ? That was supposed to be RS-232 compliant. Of the first batch of VT-220 terminals we received, the transceiver chips were replaced all but one during the warranty period. Anyway, claiming 500 m for any single-ended non-isolated system is really stupid in the real world. A balanced system like RS-422/485 could work 1000 m at 115k2 bits/s provided that the connection is isolated (no ground potential issues).
>Open collector is kinda... IEEE-488. Short distance and low bitrate.
TTL Open collector systems, such as Unibus can do about 15 m in a flat cable. However, the real show stopper is the 0.4 V noise margin in the TTL "0" state. We had to connect the CPU and each disk unit drive frames with 5 cm wide copper strips in an old building with TN-C electrification to keep the CPU/disk communication error rate at a reasonable level.
On Tuesday, September 26, 2017 at 4:11:37 AM UTC-7, upsid...@downunder.com wrote:
> On Mon, 25 Sep 2017 22:59:43 -0700 (PDT), whit3rd <whit3rd@gmail.com> > wrote:
> >and RS-423 with > >terminators (sold widely as LocalTalk by Apple, with third parties making > >ports that work for Windows) does good fast serial with (nominally) > >about 500m wire limits. > > Is that RS-423 (a.k.a DEC-423) shit still around ? That was supposed > to be RS-232 compliant. Of the first batch of VT-220 terminals we > received, the transceiver chips were replaced all but one during the > warranty period. > > Anyway, claiming 500 m for any single-ended non-isolated system is > really stupid in the real world. A balanced system like RS-422/485 > could work 1000 m at 115k2 bits/s provided that the connection is > isolated (no ground potential issues).
The RS-423 serial ports did take a transformer to network. The drivers, and receivers, had virtually NO problems, they were AMD's AM26LS30 and AM26LS32. Some connector wizardry was employed, and two-port backbone connectors, so any unoccupied connector got the right termination resistor applied (until you plugged something into it). The biggest problem: everyone who wired to an RS-232 plug forgot that they wanted the negative output signal.
On Tue, 26 Sep 2017 18:42:27 -0700 (PDT), whit3rd <whit3rd@gmail.com>
wrote:

>On Tuesday, September 26, 2017 at 4:11:37 AM UTC-7, upsid...@downunder.com wrote: >> On Mon, 25 Sep 2017 22:59:43 -0700 (PDT), whit3rd <whit3rd@gmail.com> >> wrote: > >> >and RS-423 with >> >terminators (sold widely as LocalTalk by Apple, with third parties making >> >ports that work for Windows) does good fast serial with (nominally) >> >about 500m wire limits. >> >> Is that RS-423 (a.k.a DEC-423) shit still around ? That was supposed >> to be RS-232 compliant. Of the first batch of VT-220 terminals we >> received, the transceiver chips were replaced all but one during the >> warranty period. >> >> Anyway, claiming 500 m for any single-ended non-isolated system is >> really stupid in the real world. A balanced system like RS-422/485 >> could work 1000 m at 115k2 bits/s provided that the connection is >> isolated (no ground potential issues). > >The RS-423 serial ports did take a transformer to network.
Transformer WTF ? That would require Manchester coding or similar to get rid of the DC component, not very usable for traditional NRZ signaling.
>The >drivers, and receivers, had virtually NO problems, they were >AMD's AM26LS30 and AM26LS32. Some connector wizardry >was employed, and two-port backbone connectors, so any unoccupied connector >got the right termination resistor applied (until you plugged something into it). > >The biggest problem: everyone who wired to an RS-232 plug forgot that >they wanted the negative output signal.
On Tuesday, September 26, 2017 at 10:36:30 PM UTC-7, upsid...@downunder.com wrote:
> On Tue, 26 Sep 2017 18:42:27 -0700 (PDT), whit3rd <whit3rd@gmail.com> > wrote: > > >On Tuesday, September 26, 2017 at 4:11:37 AM UTC-7, upsid...@downunder.com wrote: > >> On Mon, 25 Sep 2017 22:59:43 -0700 (PDT), whit3rd <whit3rd@gmail.com> > >> wrote: > > > >> >and RS-423 with > >> >terminators (sold widely as LocalTalk by Apple, with third parties making > >> >ports that work for Windows) does good fast serial with (nominally) > >> >about 500m wire limits.
> >> Anyway, claiming 500 m for any single-ended non-isolated system is > >> really stupid in the real world.
> >The RS-423 serial ports did take a transformer to network. > > Transformer WTF ? > > That would require Manchester coding or similar to get rid of the DC > component, not very usable for traditional NRZ signaling.
Sure did. The serial communications controller mode was called 'FM0'. It wasn't just a UART, it was kinda... smart. Zilog 8530. That was in all the Macintosh models roughly 1984-2000, so even the oldest Mac128 would do networking.
On a sunny day (Wed, 27 Sep 2017 03:16:12 -0700 (PDT)) it happened whit3rd
<whit3rd@gmail.com> wrote in
<8b01039c-7469-4161-a0e7-c6b8a761d095@googlegroups.com>:


>Sure did. The serial communications controller mode was called 'FM0'. >It wasn't just a UART, it was kinda... smart. Zilog 8530. That was >in all the Macintosh models roughly 1984-2000, so even the oldest >Mac128 would do networking.
Ah yes, good old 8530, did a Z80 based baycom packet radio modem with it http://panteltje.com/panteltje/z80/system14/diagrams/component_layout.jpg http://panteltje.com/panteltje/z80/system14/diagrams/baycom_diagram1.jpg AX25 etc ... wrote all that code in Z80 asm, 27 MHz packet radio. And I still use the TCM3105 in an RC airplane com link... was posted here years ago. SDLC HDLC... And Linux still has the drivers and docs: /usr/src/linux-2.6.37.6-p1_small/Documentation/networking/z8530drv.txt or use locate z8530drv.txt Do not see the datasheet on this PC anymore. Things change... Threw away the whole huge z80 system one day. Too much stuff...