Commodore 64: Expert cartridge loader

@DrWatson

Published in 

C64 tape formats

 · 26 May 2021

Expert loader: used by the Trilogic Expert cartridge for its freezed games. Some Alternative games (Eye of Horus...) use it too.

Expert cartridge loader

info by Fabrizio Gennari <fabrizio.ge@tiscalinet.it>

Used by the Trilogic Expert cartridge to save freezed games. Also some commercial games (Eye of Horus...) use it.

Encoding:

Threshold : $141 (321) clock cycles
Bit 0 : TAP byte $1F
Bit 1 : TAP byte $33

Data Endianess : MOST Significant bit First

Lead-In Byte : $0F
Sync sequence : $0E, $0D, $0C, $0B, $0A, $09, $08, $07, $06, $05, $04, $03, $02, $01, $00

Structure:

The length of the block is calculated from Start and End address, which is written at the start of the block (after the SYNC Byte):

 00 Start Address of data (Low, High byte) 
 02 End   Address of data (Low, High byte) 
 04 Data 
 05 Checksum (sum of the Data bytes + 1 for each Data byte, modulo $100 (256))