Posted By
gerliczer
on 2016-09-19
04:49:11
|  Re: What would I do differently in the Plus/4
Processor: complete 8 bit I/O port, overflow and NMI input, optionally capable of running at up to 4MHz.
TED: all timers programmable to be free running, repeating or one shot, and some even be cascaded; 15 levels of volume plus off, equal volume steps, 12 bit pitch control retaining original design, optionally independent noise channel; retaining VIC-II clock divisors (PAL 18, NTSC 14) and 63 cycle rasterline length; double speed data fetch, so there's only one badline and less stolen cycles (I know, it depends on RAM speed, too); additional IRQ input instead of not implemented light pen interrupt; linear luma levels.
System: no unique, nowhere else used components like 6529B, TIAs, 6510T, 2mm contact pitch expansion port connector, etc. (joystick and datasette ports may stay); DMA, NMI and RAMEN input lines on expansion port; DMA and RAMEN logic implemented, memory expansion support in KERNAL with physical implementation guide; proper joystick port design with autofire compatibility; user port pin-out backward compatible with C64, all ACIA control signals connected; possibility to hide I/O area (using the additional processor I/O pin).
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