Date   : Wed, 25 Oct 2006 17:35:44 +0100
From   : mu.list@... (Mark Usher)
Subject: ADFS sector checksums

This is how the checksum is calculated in Acorn's Superform program

 P%=buffer%+1000
 [ OPT2
 CLC
 LDY#&FF
 TYA
.L1% 
 ADC buffer%+255,Y
 DEY
 BNE L1%
 TAX
 DEY
 CLC
 TYA
.L2% 
 ADC buffer%-1,Y
 DEY
 BNE L2%
 STX buffer%+511
 STA buffer%+255
 RTS
 ]
 CALL buffer%+1000