| Posted By
Retroshire
on 2020-10-07
05:58:14
|  Kernal: what is the maximum multi capacity?
At the moment I have a multikernal with Jiffydos/Stock kernal, with a switch to change.
Is it possible to use a larger eprom and burn three kernalversions on it, switchable?
For instance: Jiffydos, Stock, Diag264.
Is it also possible to change the Basic rom with an switchable eprom?
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Posted By
MCes
on 2020-10-07
10:19:08
 | Re: Kernal: what is the maximum multi capacity?
The Kernel is a 16kb ROM, so any rom that is bigger than 16k can be "sliced" in 16k segments: there is no limit....
For simplify the realization in this case I normally choose a 64k EEPROM as W27C512: it's cheap, is mechanically compatible and can be easy programmed and erased without using UV lights...
64k imply 4 "slices" (4*16=64), the slice can be selected by 2 most significant address (switches).
The 64k EEPROMs are pin-compatible with the original ROM, but if you connect the EEPROM directly to your C16 only the slice that has the highest address will be enabled, to make the slice selectable you have to connect the EEPROM but not its pin1 (A15) and pin27(A14).
On each of this 2 pins you have to solder a pull-up resistor to Vcc (PIN28) and a wire that reach a switch that can close to ground the line.
The 4 combination of the switches positions will perform the slice selection.
Remember that during the machine operation the slice has to be stable, otherwise the C16 can crash, so use switches only with C16 off or be ready to reset it.
The same concepts is applicable to the Basic ROM, but normally it doesn't be interesting as the possibility to swap kernals...
An implementation of 4 kernal: one "switch" select the normal/jiffy kernal, another one "switch" select the NTSC/PAL kernal (and also the right generation of clock frequency...)
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