Re: Analog Cell Phones]

> >

> >> The alarm industry still makes use of AMPS cell phone systems for > >> connectivity from their client=3Fs premises. In March 2006 an Alarm > >> Industry Communications Committee petitioned the FCC to extend the AMPS > >> =3Fsunset=3F date by two years to February 2010. They asserted that there > >> were more than a million analog alarm radios and they say that there > >> just isn=3Ft enough time to change all of them out by February 2008. > >> Never mind that they have already had several years to change their > >> equipment. One of my =3Fmottos=3F is: Lack of planning on your part does > >> not constitute an emergency on my part. > >> > >> > > > >The alarm industry seems to always be behind the power curve. Some of > >them still use dial pulse instead of DTMF for wireline dialing. > > > > It wasn't all that many years ago that the phone companies charged a > premium for DTMF dialing, which adds up over time. > > For an automated application, using DTMF may speed up your dialing by > a few seconds, which really dosen't matter in the end. > > I recall that one of the other arguments that the alarm industry used > was that the manufacturers had been very slow in making replacement > products available, and that replacement equipment was still in short > supply. In other words, they could not do upgrades because the equipment > was not available. > > >

One of the really interesting aspects of alarm systems it seems many of them use the Z80 CPU. I still remember some of the opcodes for that processor.

***** Moderator's Note *****

My first "real" computer was a Heath H89, which also had a Z-80 processor. IIRC, it had a nice "area move" capability that the 8080 didn't, allowing a programmer to move blocks of memory around with a single command instead of by calling a subrouting to iterate through the memory range.

I was running CP/M, and I had to modify it so that it would send EBCD code to an Anderson-Jacobson 841 printer, which I had bought at the M.I.T. surplus store: the machine was a Selectric typewriter, with solenoids on the bottom of the mechanism to allow the (RTL) electronics to drive it.

The AJ-841 used EBCD code, which is not the same as EBCDIC: it's a six-level code, which means that there are only 64 posible bit combinations, so it includes "shift" and "unshift" characters, just like Baudot. Using the shift/unshift combination gave 126 possible codes, which was enough for most use.

The Z-80's "area move" was really nice to have because I could cache a line of ASCII, move it to another memory area with a single opcode, and then put it through a translation table to get from ASCII to EBCD. In addition, I had to account for the current "shift" or "unshift" state of the mechanism, and insert appropriate codes to shift or unshift as needed. There was also a keyboard lock feature, but I didn't care about it because I only used the machine as a printer.

The weirdest thing about the AJ-841 was that the Selectric typeball was 90 degrees off from normal: if I changed the custom ball that came with it for a "civilian" ball from a regular selectric, I had to also change the ASCII > EBCD lookup table to account for the new ball having the "wrong" characters in the positions that the OEM ball used.

Since the AJ-841 had a built-in modem, I looked it up in the Tymnet compatibility list JFL, and was astonished to discover that Tymnet would support it: not only would Tymnet allow me to log on with the EBCD codes, but it would provide "on the fly" speed and code conversion when I was talking to an "ASCII" node, which meant that I could use it directly with Prodigy. Needless to say, that was before HTML and the web, when emails were _always_ text.

If I think about it for a while, I'll probably be able to remember the divisor that I had to load into the 8250 UART to get 134.5 baud output...

Ah, the good old days.

Bill Horne Temporary Moderator

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You are correct abbout the block move capability. My first system was a TRS-80 and the video was from 3C00 to 3FFF in RAM so it was easy to swap out pages even on that rudimentary graphics system.

Oh my, fun and games on that one. I pretty much knew what was on the expansion card edge on my system and used it for various project. But a friend modified the hell out of a Model III, it had quad serial ports and we re-wrote TRS-DOS to do ISAM file systems.

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