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10

There are several issues: BEQ is a two byte instruction, using a relative offset, not a 3 byte with an absolute address. The $6E JMP you used is an indexed one, with two bytes length, not three. Its parameter is a relative offset added to the X register. So for the BEQ you want to use a two byte offset, as in 27 02, to jump around. For the JMP, $7E would ...


10

In my experience, just about any rubber band can be used, in a pinch, to replace a belt as long as you make it snug, but not too snug. I'm talking about those centimeter or more wide rubber bands they use on newspapers and the like. I repaired a VCR using the rubber band around a stalk of celery. Again, these are for "in a pinch," and you might be able to ...


4

I found the solution a roundabout way by reading Chapter 7 of the HX-20 Operations Manual: 'What if you have problems?' Although my specific memory problem was not mentioned, the solution to another memory problem (garbled menu due to having interfered with protected areas of memory) is to re-intialize memory and the calendar clock (emphasis mine). ...


3

It sounds like it can be done 'directly' No, it can not. The interface hardware is not able to generate a valid TV signal. The RS232C port is a true RS232C operating as positive and negative voltage. The HX20 uses +8/-8 Volt level (*1). Voltage is generated by a TL479 step-up/down converter and used to feed the 75188 line drivers. This Voltage is way ...


3

Direct Addressing is what Hitachi used as a term for an addressing mode that takes immediate 8-bit values as address. Obviously, this can only be used to address the lower 256 bytes of memory/IO. Apparently, the HX-20 ROM already uses this memory area for internal purposes. If you don't want to interfere (or, knowing what you're doing, manipulate) these ROM ...


2

Warning I remember the HX-20 being around but have never used one. The following advice is untested. Use at your own risk! Working through information from HX-20 Wikipedia page: You can enter the Monitor by pressing 1 at the startup menu. If the BASIC ROMs are absent (#2 and #3 from the Wiki page), then the machine works fine (but without the option of ...


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