Commodore 64: Pavloda loader
The word "Pavloda" may be found printed on tape packaging using this loader/format, it is likely to be an earlier version of the more common "Super-Pavloda" described elsewhere in this document.
Found on...
Potty Pigeon, Starion, Horace Goes Skiing, Mr Wimpy, Android 2, Bozo's Night Out, Cavelon, Zim Sala Bim...
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Threshold : $14A clock cycles (tap value $29)
Bit 0 : $3F
Bit 1 : couple $1F-$1F (see ahead)
Endianess : MSbF
Pilot : Bit 0 (*2063 about)
Sync : Bit 1
Then...
2 bytes : Load address (LSBF)
2 bytes : End address (LSBF)
n bytes : Data
1 byte : Checksum, (Addition of all n Data bytes + n) & 0xFF.
In other words you need to add all n Data bytes and add 1 for each of them.
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Notes:
We see Bit 0 and Bit 1 pulses length is not usual since the first one is bigger. The curious thing is that this loader uses a rare bit reading routine...
Usually bit reading routines involving CIA timers, start one of CIA count-downs when a signal is sent on the flag line and then wait next signal. When it's sent CIA timer is read and if it did not reach 0 the coming pulse is bigger than threshold, otherwise it's shorter.
One will be Bit 0 pulse and the other Bit 1 pulse.
This loader swaps the order of these 2 operations: starts countdown when a signal is sent on the flag line, but FIRST makes the timer count down to 0 and THEN checks the flag line again. Of course if the coming pulse is shorter than the threshold, the next pulse size has no meaning since it's just used to initialize the next countdown (syncronizes the countdown with start of next data pulse). The Loader's coder decided to use Bit 1 pulse for this "initialization pulse".
Of course we may say that Bit 1 pulse is $1F and each time one occurs, the next pulse has no meaning.
