Tech Flashback: Canon DM-2500 Intelligent Organizer

Seeing as I’m not having too much luck getting to sleep, I might as well do something productive, so here comes another post. Apologies in advance if I make any mistakes …

It’s hard to imagine now in an era of smartphones that it wasn’t that long ago that even PDA’s were non-existent or unaffordable. In the early-to-mid 1990’s, in an effort to appear somewhat technologically advanced, some people replaced their pocket notebook or diary with a “digital diary”, or “electronic organizer”.

In fact, I had two, but sadly both suffered damage in one way or another and have been long disposed of. But the other day, in a thrift shop, I came across a Canon DM-2500 for a few dollars, and I thought it was worth it to buy it just to blog about it.

The “Intelligent Organizer”

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The organizer is from Canon, specifically their business machines division which is responsible for desktop calculators and the like. This unit came with its box, but was otherwise missing all of its documentation. At least, we get to see the box which boasts a list of features which doesn’t seem so remarkable today, and a picture of the unit itself.

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The rear of the unit makes a very honest depiction of the features and how it looks on screen. That’s far from what can be said about many advertising materials nowadays … The unit is Made in China.

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To appeal to international markets, the same text is written in a variety of languages on the other sides of the box.

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2016082311298244The unit has seen some work, so it’s a little scuffed. It boasts a 10Kb RAM memory, and has a slot cut in its cover so that the function buttons and search are accessible through the cover. This means that for simple “reference” purposes, the cover doesn’t need to be opened, whereas when programming is desired, the cover is opened and that exposes the QWERTY keyboard and programming function keys.

The unit itself is almost the size of my 5.5″ smartphone, both in footprint and in thickness. It weighs slightly less at 84.65 grams, but this is 20 years of progress in a picture.

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Opening up the cover, we see the quick reference label on the inside panel. This is necessary as some of the organizers have fairly complicated features, and thick manuals to go along with it. Having the basic instructions available at a glance helps you to work the device when you’re “away from home”.

A QWERTY style keyboard is available, made of the rubbery buttons you find on older calculators. It’s not particularly tactile, but serves for more convenient text entry. The symbols available are hidden behind the SYM button, and everything is in upper case. Rather annoyingly, the PROG button is where you might expect backspace to be, so when correcting errors, you might instead exit the programming mode and destroy any progress you’ve made in programming a record.

Because of the close spacing of the buttons, and the slightly awkward layout, it’s not an easy job entering text. It doesn’t help that the unit seems to lag as well, and the LCD refreshes slowly, so it’s really a thumb board for a one-by-one character entry. Not so good for long addresses.

Some later units had additional features, such as free-form notes, redefinable fields for the address book, expenses lists, data exchange, etc.

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The rear is somewhat scuffed as well, but features a screw-down battery hatch requiring the use of three CR2032 cells, two for main and one for back-up. There is a reset hole to reset the memory of the unit and erase all data, and there is a piezo buzzer hole to let the sound out of the case.

As such organizers pre-date the availability of Flash memory, they all almost universally use SRAM which requires power to retain data. It is a volatile type of RAM, and hence this is why battery replacement can be such a daunting task. Get the polarity wrong, or remove the wrong combination of cells, or take too long while replacing the cells and all your data is lost.

To combat this, some units had their own data ports for data transfer to a PC (additional cable and software at an additional cost) for back-up purposes. This unit doesn’t have any of these features. However, because of the risk of sudden data loss, I can’t think too many people would have favoured such units over “physical” diaries which don’t have this potential for catastrophic data loss without an easy back-up option.

Features

It seems like the unit may have seen better days, as the LCD has some scratches on it and it doesn’t have particularly good contrast unless viewed from an oblique angle. I will continue anyway, but apologies for the slanted LCD images.

When powered on, the first thing you are welcomed with is the clock.

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It’s good to see that even though it’s probably an early 90’s product, it still appears to be Y2K compliant. Pressing on the TEL button allows us to look at the phone directory.

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We are prompted to search, so if you enter a few characters and enter, you can search by name, or you can just press the up-down search keys to scroll through the whole database “rolodex” style.

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The display consists of one dot-matrix line, and two 7-segment lines, no doubt a cost-saving measure to reduce the complexity of the device and also reduce its cost. Field information is displayed in fixed segments underneath. More expensive (and later units) have full matrix displays which can render bolder text, lowercase text and more natural numbers.

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The whole character set can be seen in the above images, and there really aren’t that many characters (45 in total). Everything is only available in upper case as well. To program a new entry, we can press the PROG button which briefly flashes up the capacity where U stands for bytes used, and E stands for bytes free.

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Then it prompts you field by field and you enter the data followed by enter until the record is complete (Name, Company, Address, TEL1, TEL2).

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The schedule feature is not particularly interesting. Each schedule entry is a line of text, a start time/date pair and an end time/date pair. Optionally, the alarm “flag” can be set to have the unit warn you of the event. I guess this is one big advantage of having an “electronic” diary – the possibility for alerts.

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The calculator is a 10-digit “regular” calculator with no special functions. A regular desktop calculator is more functional owing to the traditional keypad layout which is faster and easier to use.

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The calendar feature is a bit “lame” as it’s basically a week-by-week view of the dates, using both rows of numeric segments to display the days owing to space limitations. It’s hardly practical by any stretch of the imagination.

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You do have a world-clock feature, which is useful for travellers and those doing business in different countries, but it’s probably got a few out of date timezones now, due to changes which happen occasionally.

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The alarm feature is not anything special either. You get one alarm, that’s it.

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The “secret” area is basically a partitioning scheme where any data stored in the modes in the secret area is only visible once logged in. It’s probably handy to protect your data from occasional prying eyes, but there’s no way to change the password once set … so lets just hope nobody oversees you typing it in because it’s not covered by asterisks either!

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Once logged in, the “key” icon appears in the corner to let you know that any actions are being performed in the secure area. Pressing on the secret button logs you out back into the openly accessible area.

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Capacity

One thing that’s not very commonly discussed is the issue of capacity. In the period when the units were sold, aside from the “features” on the box, the next most common parameter to compare was the capacity stated in kB. I’ve seen units from 2kB through to 256kB, and formerly owned a 2kB and a 64kB unit. But how much can you actually get out of that is not clear – depending on how the data is stored, you could make more or less of the available RAM. As a result, I conducted a few calculations and experiments to flesh it out.

Available Capacity

A capacity of 10kB should equal 10240 bytes for storage. According to the screen post-reset, the unit has 10048 bytes available, so it’s likely 192 bytes are taken away for the system’s internal usage (e.g. storing the password, storing the fixed alarm, storing the calculator memory, last timezone displayed).

Record Sizes

A telephone record has the following fixed maximum field lengths:

  • Name – 24 characters
  • Company – 24 characters
  • Address – 48 characters
  • Telephone 1 – 24 characters
  • Telephone 2 – 24 characters

This totals to a record length of 144 bytes maximum. Upon storing a maximum length record, I saw a total of 153 bytes stored, thus there is an overhead of 9 bytes per record, which probably is used to separate the fields (5 bytes), and perform other administrative tasks.

Record lengths are not fixed length. I tried storing a record with a single character name, and null values for the remaining and ended up with 10 bytes used. This indicates a semi-efficient use of memory.

A schedule record has a 48 character field, with two time values recorded. Storage decreases by 60 bytes for a maximum-size schedule record.

As a result, with 10240 bytes available for storage, you could store 66 full-size phone records and two full size schedules with 22 bytes to spare.

Bytes? Really?

Because of the limited character set of just 45 characters, I’m not sure that they 10kB they talk about means 8-bit bytes at all. After all, 64 possibilities can be expressed with 6-bits, so each character can be stored in 6-bits. For the case of a numeric digit (TEL1/TEL2 fields), they have just 10 possibilities, so can be stored in 4-bits (e.g. BCD).

If 8-bit bytes were used, then the top two bits are practically free to be used as flags, and might be for indicating secret/non-secret data, helping with deletions to “defragment” records or to indicate active alarms etc. If they were not used, then it could be a bit of a waste.

If BCD was used to store the numeric phone numbers, then the TEL1/TEL2 fields would essentially be the same size as the Name field (assuming 8-bit bytes for text), and that might explain the 10kB “claimed” capacity which isn’t really a power-of-two value, although it would quickly come undone if I started storing all text and no numbers in the phone book. Alternatively, the SRAM memory might be made by combining 8kB + 2kB dies.

Teardown

Here, we get to the possibly fun part – the taking apart “part” of the post.

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2016082311368273Under the battery hatch, the warnings about battery replacement are repeated. They’re even repeated on a piece of transparent plastic on top of one of the batteries. The serial number and date code are on the inside of the cover as well.

While all seems to be well, the unit wasn’t in the best condition as the previous owner had replaced the cells with Energizer cells, and then forgotten about the unit. While I’ve never seen a lithium coin cell leak, I definitely saw one now. I actually spent a bit of time cleaning the mess and scraping off some of the corrosion to get it to work again. Note the central contact.

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Two screws on the edge hold the cover in place, along with some internal clips. The internal PCB shows some SMD components, a few diodes to prevent mishaps in case of batteries running down or being inserted incorrectly, a tanalum capacitor and gob-top “chip on board” type construction.

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The LCD is connected by a many conductor flexible cable that’s probably fairly brittle, so I didn’t touch it. I didn’t take it apart any further, as the other side would have predictably been the keyboard printed trace pattern.

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The rear cover houses the piezo buzzer under a bit of tape. That’s basically it.

Conclusion

I suppose that in the early-90’s when anything digital and computer related was considered advanced, these units may have been considered “cool” and in some ways, the “poor man’s PDA”. Unfortunately, while they helped some people “go paperless”, they needed a battery change roughly every year which comes with a risk of complete and total data loss if not performed correctly. They were also relatively cumbersome to use as the data entry was slow, and the forms of data that could be stored were relatively limited compared to pen and paper. There were advantages in security, reusability and in having schedule alarms, but some units were also very pricey and difficult to use without having the manual. They were also vulnerable to everything that electronics would be vulnerable to – external EMI could cause some units to lock up and freeze, requiring a reset that could kill off all the data as well. In all, I suppose their “lack” of universal popularity probably explains just how impractical these might have been compared to a good “pen and paper” diary or notepad.

About lui_gough

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4 Responses to Tech Flashback: Canon DM-2500 Intelligent Organizer

  1. sparcie says:

    I suspect the overhead bytes in the records are probably recording the lengths of the various fields in order to allow for the variable length. Another possibility is they are null terminated.

    I suspect the only reason they’d work in terms of bytes is convenience in writing the program code, and that the processor and memory they used was probably 8 bit. It’s actually a bit of effort in terms of firmware code to store symbols in 6 bits where the word width is 8 bit. Also on the marketing side of things, KB was a commonly understood term, other measures may have been confusing to the general public.

    Sparcie

    • lui_gough says:

      Nice to hear from you again!

      Indeed, you might be right. I did think the data could be stored as a stream with a terminating character … but the overhead is 9 bytes with 5 fields … I suppose a valid guess might be:
      (start-of-record)(field1)…(field2)…(field3)…(field4)…(field5)…(end-of-record)
      but that would be 7 bytes of overhead …

      or
      (field1)…(end-field1)(field2)…(end-field2)(field3)…(end-field3)(field4)…(end-field4)(field5)…(end-field5)
      which would have 10 bytes of overhead …

      so maybe they omit the end of the last field and use the header for the next record as a delimiter.

      To be honest, I have not a clue how it is implemented, but it was just that the overhead of 9 bytes just seemed an odd number to me.

      And yes, definitely agreed that character sizes not matching bus widths makes for an awkward buffer/rotate issue which is costly – so I presumed the excess bits might be used as flags … with 2 bits, four flag combinations can be had. Maybe one is used to denote the data is secret … or maybe that’s done with different field delimiters …

      If they really could spare the processing, they might have even gotten more storage through using Varicode style encodings which have frequency-based bit sequences … albeit even more complex than a reduced size character storage.

      I suppose I just like to think about these things. I wonder how much working RAM it has, if at all, or if it “works in place” and that might explain the 192-byte overhead from a blank state … maybe it uses it as a working buffer for record copies when records get deleted and everything needs to be shuffled around.

      – Gough

  2. Mark B. says:

    I see some tautology in “It boasts a 10Kb RAM memory”, as RAM already stands for Random Access Memory.

    And by the way, an unpopulated place for a gob-top IC looks interesting. I guess that could be some additional RAM.

    • lui_gough says:

      This “tautology” courtesy of Canon, as printed in numerous places on the organizer itself.

      It could be a place for additional memory – left unpopulated to differentiate between different models … or maybe it depends on their source of chips. Maybe they have a slightly different bond pad layout for their other supplier, so they decided to have different sorts much like how some PCBs have multiple footprints for things like voltage regulators so that they can accommodate variations.

      – Gough

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