 .PAGE 'CHCKSUM'
 *= $CF00
 LDX #$FF
 TXS
 CLD
 SEI
 LDA #0
 STA DCHKSM
 CMP DCHKSM
CHKPRO
 BNE CHKPRO
 LDA #$D0
 JSR CHKSUM
 STA DCHKSM
 LDA #0
 STA ECHKSM
 CMP ECHKSM
 BNE CHKPRO
 LDA #$E0
 JSR CHKSUM
 STA ECHKSM
 LDA #0
 STA FCHKSM
 CMP FCHKSM
 BNE CHKPRO
 LDA #$F0
 JSR CHKSUM
 STA FCHKSM
 JMP *
;
CHKSUM ;.A=ADDRESS
 CLC
 PHA
 STA TEMP+1
 LDA #0
 STA TEMP
 LDX #16
 LDY #0
CHK1
 ADC (TEMP)Y
 INY
 BNE CHK1
;
 INC TEMP+1
 DEX
 BNE CHK1
;
 ADC #0
 STA TEMP+1
 PLA
 SEC
 SBC TEMP+1
 SBC #0 ;.A=CHECKSUM BYTE
 RTS
 .END
