Re: Adding ports via slotexander

[JP Grobler]

Hi   Say for example I want to add another vdp etc and access it via a port number in() out () how is this done in hardware.   JP On 6 Jun 2001 19:15:14 +0200, [EMAIL PROTECTED] (Hans Otten) wrote:   >Hi, > >You have to explain what you mean with 'additional port'. > >A real slot expander expands a primary slot to max 4 expanded slots. In >there memory can be switched to the z80 by the slot hardware. >This is memory space, not i/o space as is used for i/o ports. These are >limited to 256 in total whether a slot expander is used or not. All >cartridges in any slot and internal devices are always 'i/o port active' at >the same time. > >An example of a fake (not real) slotexpander is the Elektuur design which is >nothing more than eight parallel wired slot connectors of which only one at >a time is made active with the slot select signal. Handy to avoid replacing >cartridges (and to avoid a cartridge from starting at boot time by making >that slot inactive, grab ROMS!). By the way: when building this Elektuur >device: add the busdir  signal and remove the databus buffers. > >Ofcourse it is possible to add a third slot connector by getting a connector >in parallel with one of the existing slot connectors and replace the slot >select signal with the appropiate slot select signal out of the computer, >primary (MSX1) or secundary (MSX2, where  internal slots are expanded most >of the time. > >In theory: You can have two slots completely wired in parallel, insert a >only ROM based cartridge in one and only i/o based in the other. But how are >you sure it is pure ROM or i/o? Not recommended, the chance of having >conflicts is big. >