Commodore 64: Turbotape 250 loader

@DrWatson

Published in 

C64 tape formats

 · 3 years ago

Found on...

• Giana Sisters
• China Miner
• Crazy Cars 3
• Hollywood Poker
• Siren City
• ...etc

'Turbotape 250' uses two block types..

The first is the Header Block which is normally 192 bytes long but can be less (I've only so far found sizes of 192 and 22), and it contains information for a following Data block.

Threshold : $21 ($107 clock cycles).
Bit 0 : $19
Bit 1 : $28
Endianess : MSbF

Pilot byte : $02 (various quantities)
Sync : $09 down to $01

Then...

1 byte : ID...

• $00 for DATA block.
• $01 for HEADER block (BASIC type).
• $02 for HEADER block (PRG type).

For HEADER blocks the following data is sent after the ID :-

• 2 bytes : Start address of data (LSBF)
• 2 bytes : End address of data (LSBF)
• 1 byte : Whatever $00B0 contained at the time of saving
• 16 bytes : Name (PETSCII chars)

After this there MIGHT be more bytes, which are filled with value $20. Some save routines save up to 192 bytes for Header (the space after Name is always filled with $20).

For DATA block there is data (length is in the Header) immediately after the ID byte.

After the Data there is an XOR checksum byte, which is XOR of Data only (not ID or anything else)...

Note
Header does not have this XOR checksum.

Sometimes has a trailer of Bit 0's.