+Al_Nafuur Posted January 17, 2022 Share Posted January 17, 2022 The last few days I have been dealing with a strange behavior of the VCS 6502 hardware (Maybe this behavior is commonly known, but it took me a few days). I want to add @cd-w's 24 char textkernel to display the online HSC table in 1942 bB. One part of the HSC table screen data is in ROM (the title rows) and the other part is in SC-RAM (the table). The base address for the indexed read is in SC-RAM and if I want to display a row from ROM the index is greater 127 and the page boundary from SC-RAM to the first ROM page is crossed. This takes only an additional cpu cycle and works fine on the emulators (except for a wrong scanline count). But on the real hardware it looks like the low byte of the new address is set in the regular cycle and the high byte in the additional. Unfortunately the first of these two cycles looks like an access to the low byte of the same page for the cartridge, which is in our case (even more unfortunately) the write port of the SC-RAM, so the cartridge takes whatever is on the data-bus at then end of this cycle and writes it to the SC-RAM! textkernel_HSC.asm textkernel_HSC.asm.bin Quote Link to comment Share on other sites More sharing options...
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