Tuesday, August 15, 2017

68HC11

My new to me 68hc11 board is waiting at the post office!  It's a much wanted (I don't NEED it mind you) replacement for the one that was damage in a fire.  For under $15 off of ebay shipped, that's a bargain if it works!  I'm guessing this is based off of the Buffalo monitor ROM.

Expect a 68hc11 version of Microsoft like BASIC in the future (yet another project to divide my time further)  There aren't going to be a lot of changes to the main interpreter.  Memory moves won't need to use the stack pointer, I can dedicate the Y register to pointing to the next character for large sections of the interpreter.  I/O would have to completely change though.  The bit banger cassette I/O will probably be replaced with an IDE port and simple DOS.  Video out and keyboard will be through a terminal (Buffalo calls?).  I may decide to stick on a V9958 and PC keyboard interface.

The hc11 has a few added instructions that may come in handy.  The hc11 supports XGDX like the 6803 and XGDY which might allow the use of X and Y for temporary storage without having to use direct page RAM in a few places.  It's only a space saving optimization if I'm storing 8 bit registers in X as it takes 3 clock cycles and using Y requires 4.  It would be faster or the same speed to save D in X though.  Y requires 2 byte opcodes, so it's slower than X and slower than using the stack pointer.but you don't have to disable interrupts like with the stack pointer. It's definitely faster than constantly changing X.

There is a version of GCC for the 68hc11, so that's a definite improvement over the 6803.

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