Well this is awkward
Looking back at the schematic, did anyone spot the deliberate mistake?
It's on the bottom left side of PortaCore.
No? ATN is not connected to anything. This is internally connected to the Z80's NMI line. There are two problems with it being unconnected. One is that it means PortaBit can't fire the NMI pulse to trigger the on-screen menu. It also means that the pin is floating, which could mean frequent misfirings of the Z80's NMI routine.
This presents problems as the majority of the firmware work centres on the on-screen menu. But there are a couple of solutions.
One is that I could run a wire from pin 34 (ATN) of PortaCore to an unused pin on PortaBit, RC5 for example. The problem with this is that the pin pitch of both chips is tiny, which makes it difficult to solder. And since they are both unconnected, this means there's no trace (or more importantly, vias part way along it) to solder to.
The other approach (which I'm probably going to use) is to delete one of the status pins (PORTABIT_S0 to 2) and remap the NMI line to the pin it formerly occupied. This would put ATN on pin 14, which is currently shown by S2, which is traced through to RF7 on PortaBit.
Oh well. Nobody's perfect.
It's on the bottom left side of PortaCore.
No? ATN is not connected to anything. This is internally connected to the Z80's NMI line. There are two problems with it being unconnected. One is that it means PortaBit can't fire the NMI pulse to trigger the on-screen menu. It also means that the pin is floating, which could mean frequent misfirings of the Z80's NMI routine.
This presents problems as the majority of the firmware work centres on the on-screen menu. But there are a couple of solutions.
One is that I could run a wire from pin 34 (ATN) of PortaCore to an unused pin on PortaBit, RC5 for example. The problem with this is that the pin pitch of both chips is tiny, which makes it difficult to solder. And since they are both unconnected, this means there's no trace (or more importantly, vias part way along it) to solder to.
The other approach (which I'm probably going to use) is to delete one of the status pins (PORTABIT_S0 to 2) and remap the NMI line to the pin it formerly occupied. This would put ATN on pin 14, which is currently shown by S2, which is traced through to RF7 on PortaBit.
Oh well. Nobody's perfect.
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