hardware

The 16550 UART was the first chip to be attached to the CPU bus that does not have a native 65xx bus interface and hence needed a little more effort. The reset and interrupt signals are active high, while the 6502 needs them to be active low. So reset needed to be inverted, and interrupt is driven through a 74LS06 inverter driver with open collector outputs in order to be able to be wire-ORed to the system interrupt line.

Our current audio/video board is based on the Yamaha V9958. The V9958 is the successor of the V9938, which in turn is the successor to our TMS9929/9918, which has served our project for quite some time. But it is hard to ignore what the V9958 has to offer (80 column text mode to begin with), so we decided to use it as the first major upgrade to the Steckschwein Hardware specs in a couple of years.