I recently stumbled upon TurboGrafx-16 Schematics and was slightly surprised to notice that the #CE signal on the HuCard port is in fact A20 from the Hu6820 CPU. I decided I wanted to see more of this and this put my TurboGrafx-16 under the oscilloscope. Luckily, my latest PC-Henshin PCB has a nice 0.100" pin header footprint with all the relevant HuCard signals directly on there. This made probing extremely easy!
I put PC Genjin in the PC Henshin and probed away! Capture 1:This shows a sequential 4 byte access. Triggered by falling edge of #OE. Capture 2:This shows a sequential 4 byte access, except here we see that only the last 3 byte reads are to the HuCard because #CE was high during the first byte read. Capture 3:This shows that #CE and A0 have the same pulse width which makes sense since #CE is technically the most significant address bit. |
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