GO128 ?

[Mark Smith]

Is there anyway to jump back to 128 mode from 64 mode ?  Without resetting ?

Thanks

Mark

[Blacklord]

Is there anyway to jump back to 128 mode from 64 mode ?  Without resetting ?

Thanks

Mark

No - as far as I know, this was a question that I asked many, many years ago & always got the negative response. Mind you, we could always ask Bil Herd - he frequents this forum

cheers,

Lance

[Mark Smith]

No - as far as I know, this was a question that I asked many, many years ago & always got the negative response. Mind you, we could always ask Bil Herd - he frequents this forum

cheers,

Lance

Hmm ... well we could ask him .. and if he also gives a negative answer we can also blame him!  ... Kidding! ;-)

[airship]

I've been reading, re-reading, and re-re-reading the'C128 Programmer's Reference Guide' and 'Mapping the Commodore 128' every night for two weeks, and one thing is emphasized and proven over and over again: you can't get there (C128) from here (C64).

Though it IS possible to do a manual warm reset (hold down the Run/Stop key and hit reset) while preserving all but pages 0 and 1 in RAM. So at least that's something. (Page 410, C128-PRG, holding the Run/Stop key drops you into monitor mode on warm reset.)

Code example from C64 mode:

900 (READ, POKE loop to set up M/L entry point for C128 code)...
1000 PRINT "Please hold down Run/Stop key and press the reset button. When you see the green screen, type 'G $C000'. Thank you!"

[Andrew Wiskow]

If you have a Lt. Kernal Host Adapter connected to your C128's expansion port, along with the required 128 Daughterboard correctly installed, then, and only then, can you use GO64 to go to 64 mode from 128 mode, and GO128 to go to 128 mode from 64 mode.

With a standard 128, however, the answer is no.  Of course, that little reset button on the side of the 128 is a handy way to go back to 128 mode.  

-Andrew

[BilHerd]

Hi All,

I specifically made it a one way trip into C64 land as I didn't want to create a "different" C64 mode.  If you think of it like a song someone else wrote or something that was copywrited, the definition of what a C64 was wasn't mine to change.  Things that had reset lines attached to them like the MMU were safe to make go away (I had someone at a CES assure me that he was smart enough that he would have found a way to make it still appear in the map, which means he missed the point, making it go away was harder then leaving it in) but the stupid fast bit in the VIC was one that I left in not meaning for it to be used even accidentually.

  I was more paranoid that day that if we made the VIC remove the fast bit that we would be stuck upon occasion in C128 mode and the fast bit would still be missing as there was no reset line to the VIC chip (24 year old memory here, I might be wrong in which case I must have had a different reason).  I could have asked for a special write pattern (write aaa then bbb, etc) to "unlock" and "lock" but during the 5 seconds that it took me to make that fateful decision I thought of the revs of software in the development pipe, the delay time before the next rev of the vic would hit, the need to synchronize the ROMS to the vics and the fact that it might induce a show stopping error into that rev of the vic chip.  

So basically if I made a C64 mode with any (intentional) registers including escape to 128 mode or mmu banking I might promote a C64+ game that wasn't C64 compatible which sounded bad to me.  I know Freddy Bowen was something of a purist in this also though I don't recall asking him about this.  I do recall standing in his office while he got out a real C64 because he liked to play "escape from Fractalus" which as it happened was the game that smashed the fast bit because they transfered 256 locations to write to the first 32 and because I wasn't patranoid the day I left that in.

Believe it or not we argued about whether to have a reset button, it made things more complicated trying to figure out a warm start from a cold.  I heard that later they used a register in the 80 column chip to determine if it was a cold or warm start.  We tried writting patterns to memory but found a brand of dram that kept memory the memory pattern  50% of the time for 8 seconds

Bil Herd

[Blacklord]

Bil,

The other couple of things that work out nicely (& probably not as intended!) are the numeric keypad & the hack that allows the 80 column screen to be written to by C64 mode. I'm guessing neither of these were intentional ?

cheers,

Lance

[airship]

When we tested the C128 at INFO, we were blown away by just how compatible the C64 mode was.

If you recall, Benn's biggest issue with the Plus4 was that it was incompatible with the 64, so he was a stickler on this point. Since we had just about every piece of software ever written for the C64, he loaded and ran just about everything we had, and the C128 was rock solid. Not a glitch. 100% compatible. We were impressed.

So good work, Bil! You guys created the best 8-bit computer that will ever be.