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Thread: Epson HX-20 from Bundeswehr, some questions about unusual memory expansion and so on.

  1. #1

    Default Epson HX-20 from Bundeswehr, some questions about unusual memory expansion and so on.

    Hi. It's my first post on the forum so i'd like to explain some things.
    I live in Poland and when i found Epson HX-20 on local auction portal for 150zł (less than 50$) i couldn't resist.
    I bought one from the guys who are specialized in post military (demobilized) equipment.

    I have some questions about it.
    First is how it was used in military? Anybody has any ideas? I heard that HP41 calculators were used onboard flying tankers to calculate things like center of gravity. Some people reports about various programmable calculators from 80s that have been used as MBCs (Mortar Ballistic Computers).
    But how was HX-20s used in Bundeswehr? I'd like to know what was the use of the device i have.

    I found this one quite unusual. First are the ROM modules that turns out to be EPROMs with stickers on them (they seems to protect those little windows from UV radiation like it used to be with EPROMS). I heard that orignal ones had mask one time programmable PROMs and no EPROMs like mine have. I am talking about ones that stores firmware with BASIC interpreter and so on, the extra EPROM slot is free (there is no chip in it).

    The unusual thing is the rater exotic memory expansion board that fits inside. It's smaller than the other internal expansion boards i seen on internet. It seems to use 2 SRAM chips and regarding to datasheet they have 32kB each so it gives 64kB total.

    Epson HX-20 can adress only 16kB of memory trough it's expansion port (it has 16kB of RAM by default so when you connect expansion it gives total of 32kB RAM).
    This leds to conclusion that there must be software switching implemented (there are no DIP switches on the board) to utilize this 64kB of memory and turn them into banks of 16kB.

    The interestning thing is that the module has to be "activated" trough a specal procedure printed on the case. Before activation HX-20 shows 12891 bytes of free memory available to user so it's like any unexpanded HX-20. After going trough procedure it shows 29275 bytes so it's like HX-20 with expansion unit.

    So the questions are:
    -How it was used in Bundeswehr?
    -How to utilize software switching to use the enteire memory in this unusual memory expansion unit?

    Below there are photos of the memory expansion board and expansion unit activation procedure.

    IMG_4142.jpgIMG_4144.jpg

  2. #2

    Default

    I am having quite a lot of fun when programming this thing. I'd like to share with you one of my first programs i have written. I have updated this program many times and yesterday aswel as today i have spent some time on thinking what could i add to it.

    The program is a tenkey type calculator. It is written from scratch and very different from the one that is already available on the net.
    -It has automatic trace print function and manual printing functions for result and keyboard register.
    -It has 120 memory cells you can use in read/write operations.
    -It has statistical module for statistical calculations (count, min, max, diff between min and max, sum, mean) and can also plot a simple bargraph.
    -It can be used as framework for you'r own programs so you can run your own programs inside it. Just input your program between certain lines and press certain key to start it.

    The downside is that i can't really tell how it will work on keyboard variants other than German. But it should be very easy to modify.
    I am publishing this as free software OFC so feel free to edit it and use any way you want.

    Software is distributed with manual. Software itself is a MP3 file. Instruction on how to transfer it to HX-20 is provided, you just need jack to jack cable and OFC HX-20 to do it. I am unable to provide listing online as i still have not made my RS-232 cable and i have no Linux to use "HXtape" program.
    If you want to list it you would need "HXtape" program or just use your HX-20.

    Here is a link: www.macieksoft.cba.pl/softw/hx20/tenkeyhx20.zip

  3. #3
    Join Date
    Jun 2016
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    Guisborough, England
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    Hello,

    I've got an HX-20, still just about working, apart from battery (using external rechargeable ones just now).

    My unit has an internal RAM expansion, this also requires a initialisation routine, with a set of commands within the MONITOR process. Seem to be very similar to the instructions you have. May not be identical?

    The unit can cope with 64k memory total.

    Normally, this comprises 16K ROM, and the default of 16k RAM. There are sockets for two extra ROM chips, going from 16k to 32k (my unit has one rom socket with a FORTH programming ROM installed). The RAM can be filled up to 32k either with the external RAM expansion, or with the internal unit (seems there are at least two types).

    Loading software via MP3 file?? That's a new one. I'll get the file and check that out!!

    I've also got the Epson TF-20 floppy drive unit, which DID work well, but now it does not connect. Maybe damaged the PCB in the HX with constant connect/disconnect of cable socket. TF still seems to go though the motions of booting, etc, so I think it is working otherwise.

    Regarding your RAM card, the only option I could think of is that there might be a way to switch OFF the ROM and use the RAM instead??

    Geoff

  4. #4
    Join Date
    Jun 2016
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    Guisborough, England
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    Hm, just checked.

    The instructions re MONITOR are quite different.

    Mine relate to disable of one of ROM sockets to free up for RAM.

    My instructions use two byte addresses, i.e. FEFD or FE99, while your instructions refer to single byte addresses 7E and 3B (at the other end of memory??

    Geoff

  5. #5
    Join Date
    Jun 2016
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    Guisborough, England
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    Hmm, bit of a mystery here.

    The HX external expansion provides either 32k extra ROM or 16k ROM and 16k RAM.

    Not sure how the extra ROM fits in.

    My 16k RAM board is actually providing 8k extra ONLY, as the FORTH ROM is active. If I switched that off, then I could get the 16k extra RAM.

    The manual shows the max memory as 64k, i.e. 0000 - FFFF. 16k RAM, 8k not assigned, 8k 'option' ROM (which is where the FORTH sits), then 32k of ROM for BASIC, and I/O routines.

    What shows on your MENU when you turn device on?

    Geoff

  6. #6
    Join Date
    Jun 2016
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    Oh, that link for the 'tenkey' prog seems NOT to work any more?

    Did you get a copy of the file?

    Geoff

  7. #7
    Join Date
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    Doing some quick check on the web, there seem to be other machines on offer. One listing refers to use on Bundeswehr aircraft, but not what about.

    Further digging might reveal. Also, try to check what's in the ROMs?

    Geoff

  8. #8
    Join Date
    Jun 2016
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    Guisborough, England
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    Well, I've never seen reference before to 'memory banks' for the HX....

    Trying to check in my manual for what the addresses are for on the initialisation, I find some details for the first one, 7E. The indiv bits for this byte indicate certain things. Bit 4 shows 'currently selected memory bank'!! What constitutes memory bank, I don't know, but seems there in Bank 0 and bank 1, and this bit can of course be 0 or 1 and that's the current bank. The info suggests enter 8?, but I cannot make out what the second char is, maybe it's a special German one. Capital O (Oh) with two dots above? So change may be to swap from Bank 0 to Bank 1?

    Geoff

  9. #9
    Join Date
    Jun 2016
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    Well, according to further checks via web, there do seem to be a number of these units on the market just now, some with extras, others less so.

    Does your's have the microcassette drive? Does the drive work?

    The Memory expansion unit would seem - from pics on the web - to have two sockets added. This is NOT normal. Any idea what the sockets/connectors are for? Any idea what chips are in the expansion unit (as opposed to the chips in the main unit)?

    What's the state of the battery in your's? Proper repl batteries are not easy to find nowadays, I'm using an external battery pack with mine.

    Geoff

  10. #10

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    Yes, mine has microcassette drive and it works just fine, i have used it multiple times and i never got any troubles with it. Tape head seems to be in perfect condition.
    Orignal (Epson) external memory expansion unit has 2 sockets that are empty by default. From what i have read they are for extra ROM modules, you can fill this with your own ROM, AFAIK it can be set trough microswitch to "replace" orignal ROMs.
    I don't own orignal external expansion unit. The device in ex Bundeswehr ones that looks like expansion unit (it has even written "expansion unit" on the case) is actually a charger in a case of expansion unit. This charger has 6.33V output (measured without load) and when current reach 1A it goes into CC (Constant Current) mode. It also has extra socket (probably for a lamp) that is about 30V without load. There is also a socket at the left side, i don't know what it is for, it has unusual 3 pin connector.

    When i bought it battery was leaked. It was described as untested. I used to use 4AA batteries externally to power it, however printer causes quite high current spikes and it shows to charge battery when i use it. So when i need to print i just use lab power supply. When you quickly disconnect batteries and connect lab power supply you won't loose data from RAM.

    Link worked in Mozilla, but in Chrome some graphic from a hosting provider just showed up.
    You can also try https://www.macieksoft.cba.pl/softw/hx20/tenkeyhx20.zip

    However now i am preatty sure that it will require some changes in code as i used many INKEY$ statements that reference German keyboard chars.

    EDIT:
    Proper repl batteries are not easy to find nowadays
    I heard about a people who have made their replacements with NICD or NIMH sub C cells. Orignal NICDs were sub C sized.
    The problem with NIMH ones is that they seems to have less tolerance for overcharging than NICD. Epson HX-20 has no peak detection at all. Charging circuit is literally 2 elements. Just resistor and a diode. This is why it is important to respect maximum charging time which was orignally 8 hours for a fully discharged battery. From what i recall PX-8 or PX-4 had better charging circuits, but in HX-20 it was as simple as it could be.

    Further digging might reveal. Also, try to check what's in the ROMs?
    Mine has no extra ROMs. The ones that it has seems to be orignal ROMs, however thay are EPROMs instead of mask PROMs. Expansion memory board i have doesn't have any ROM sockets, just 2 SRAM chips as you can see on the photo.

    The manual shows the max memory as 64k, i.e. 0000 - FFFF. 16k RAM, 8k not assigned, 8k 'option' ROM (which is where the FORTH sits), then 32k of ROM for BASIC, and I/O routines.
    AFAIK by default you got 32k ROM and 16k RAM. This gives 48k total, so you got 16k available for expansion unit.

    What shows on your MENU when you turn device on?
    When device isn't initialized (when you remove a power then after some time connect it again) it just shows MONITOR. When i initialize it (or when i turn it ON and there was no power interruption) it shows MONITOR and BASIC, then when i use TITLE statement to name one of my programs they appear on menu screen.

    Loading software via MP3 file?? That's a new one. I'll get the file and check that out!!
    It is simple. Epson HX-20 has a connectors for external tape drive, it shares same recording format as internal tape drive. Instead of tape drive you can connect any audio device capable or record and playback. PC sound card works well , you just need a 3.5mm jack to jack cable to connect. Single cable is enough because you don't need simultanous record and playback (it's not even possible anyway). Just remember to record in mono, this decreases file size and will work regardless of jack type (should work with 3 pin stereo jacks aswel as 2 pin mono ones). For recording i used free program called Audacity. For playback any program can be used. Manual i provided with my tenkey calc software describes the whole process.
    Last edited by macieksoft; October 3rd, 2017 at 07:01 AM.

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