C1/5C58: C2 31        REP #$31
C1/5C5A: A9 01 00     LDA #$0001
C1/5C5D: 18           CLC 
C1/5C5E: ED CA 97     SBC $97CA		// Subtract the value at $97CA from 1...
C1/5C61: 50 04        BVC $5C67
C1/5C63: 10 17        BPL $5C7C		// If overflow, ends up at 5C69
C1/5C65: 80 02        BRA $5C69
C1/5C67: 30 13        BMI $5C7C		// To get here: overflow clear. --------|
C1/5C69: 8A           TXA 		// If overflow, go up to BRA $5C84.	|
C1/5C6A: E2 20        SEP #$20							|
C1/5C6C: AE CA 97     LDX $97CA		// X = value which caused overflow	|
C1/5C6F: 9D BA 97     STA $97BA,X	// Value of A stored at $97BA+X		|
C1/5C72: C2 20        REP #$20							|
C1/5C74: EE CA 97     INC $97CA		// Increment. Loop suspected...		|
C1/5C77: A9 58 5C     LDA #$5C58						|
C1/5C7A: 80 08        BRA $5C84							|
C1/5C7C: 8A           TXA 		// <------------------------------------|
C1/5C7D: 22 C8 27 C2  JSR $C227C8	// Processing of second parameter?
C1/5C81: A9 00 00     LDA #$0000
C1/5C84: 60           RTS 

Key to understanding: WTF is $97CA?!