On the C64 Reloaded boards, all ROM images have been burned into a single EPROM chip. As described by Individual Computers, this ‘…gives some extra space for a second Kernal ROM and a second character set’. As I will be using the C64 Reloaded with my JiffyDOS loaded 1541 Ultimate II, I ordered a JiffyDOS kernal IC from Retro Innovations.
The JiffyDOS mod is really easy as no hole has to be drilled into the case. To switch between Kernals, the RESTORE key must be pressed for 3+ seconds. The JiffyDOS IC comes with a jumper which selects which Kernal is the default. When the jumper is removed, JiffyDOS is the default Kernal and the CBM Kernal can be selected using the RESTORE key. When the jumper is installed the standard CBM Kernal is default and JiffyDOS can be reached using the RESTORE key.
First I tested it with the the jumper removed from the C64 Reloaded JiffyDOS ROM so the machine booted directly into JiffyDOS at startup. In this mode, the standard CBM Kernal is 2nd. I then attached my 1541 Diskette Drive which had already been modified with a 1541 JiffyDOS ROM from Retro Innovations as described in the 1541 JiffyDOS Mod. The ‘@’ command showed the message of ’73,JIFFYDOS 5.0 1541, 00,00′ indicating that everything worked as expected. I got the exact same information when I did it with the 1541 Ultimate II attached. So that worked as well.
With the jumper attached, the default Kernal is the standard CBM Kernal. This is the way I like my JiffyDOS modded machines to boot. I guess it’s a nostalgic thing, but I really like being greeted by the original Commodore 64 boot screen and then I have to do something actively with the machine, like pressing a button/flipping a switch, in order to swap to JiffyDOS! The C64 Reloaded Wiki states that just pressing the RESTORE button for 3+ seconds should do the trick. However, something odd happened when I wanted to switch into the JiffyDOS Kernal. In order to do this, I had to hold the RESTORE key for 3+ seconds, release the RESTORE key and then flip the power button up (this is the reset function of the button) in order to boot the system into JiffyDOS mode. The C64 Reloaded Wiki states that just pressing the RESTORE button for 3+ seconds should do the trick. The combination of the RESTORE key + Reset switch should actually change the character set to whatever 2nd character set that is installed on the ROM chip. I have not tested this with an alternative character set as I don’t think I will ever need another character set anyways on this machine. The bottom line is that the provided JiffyDOS ROM worked as the 2nd Kernal and the dual Kernal system now works the way I like it.
As a side note, despite which Kernal is active (CBM or JiffyDOS), using the reset function of the power switch will reset the system back to whatever Kernal that was active before resetting. This is a neat feature as it is not neccesary to repeat the Kernal swap drill over and over again every time a new game is loaded.
UPDATE: Want to burn your own EPROM with JiffyDOS? Find the tutorial on how to do it here.
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