Atari 400 Technical Reference Manual page 310

ERR LINE ADDR 51 52 53 54
SIO ( SERIAL BUS INPUT/OUTPUT CONTROLLER )
PAGE 49
2113
2114 E1329 AD OD D2 LDA SERIN
iTHIS INPUT BYTE IS THE CHECKSUM
2115
E132C
C5 31
CMP CHKSUM
2116 E132E
FO 04
5EG SRETRN i5RANCH IF CHECKSUMS MATCH
2117
2118 E1330 AO 8F LDY #CHKERR
2119 E1332 84 30 STY STATUS
iSET CHECKSUM ERROR STATUS
2120
2121 E1334 A9 FF SRETRN: LDA
#$FF iSET RECEIVE DONE FLAG
2122
E536
85 39
STA RECVDN
2123
2124 EB38 68 SUSUAL: PLA
2125 EB39 A8 TAY
iRESTORE Y REG
2126 EB3A 68 PLA
iRETURN FROM INTERRUPT
2127 E535 40 RTI
2128
2129
2130
2131 EB3C AD OD D2
NOTYET: LDA SERIN
2132 EB3F AO 00 LDY
#0
2133 EB41
91 32
STA (BUFRLO)
I
Y
iSTORE INPUT REGISTER INTO BUFFER
2134
2135
EB43
18
CLC iADD IT TO CHECKSUM
2136 EB44 65 31
ADC CHKSUM
2137
EB46
69 00
ADC #0
2138 EB48 85 31
STA CHKSUM
2139
2140 EB4A E6 32 INC
BUFRLO i INCREMENT BUFFER POINTER
2141 EB4C DO 02 BNE NTWRP1
2142 EB4E E6 33 INC BUFRHI
2143
2144 EB50 A5 32 NTWRP1: LDA BUFRLO
2145 EB52 C5 34 eMP
BFENLO
2146 EB54 A5 33 LDA
. BUFRHI
2147 EB56 E5 35 SBC BFENHI
2148 EB58 90 DE BCC SUSUAL
iBRANCH IF NEW BUFFER ADDRESS IS IN BUFFER L
2149
2150 EB5A A5 3C LDA NOCKSM
2151 EB5C
FO 06
BEG GOON
iBRANCH IF A CHECKSUM WILL FOLLOW DATA
2152
2153 EB5E A9 00 LDA
#0
2154 EB60 85 3C STA NOCKSM
iCLEAR NO CHECKSUM FLAG
2155
2156 EB62 FO DO
BEG SRETRN
iGO
RETURN AND SET RECEIVE DONE FLAG
2157
2159
2159 EB64 A9 FF GOON: LDA
#$FF
2160 EB66 85 38 STA
BUFRFL iSET BUFFER FULL FLAG
2161
2162 EB68 DO CE BNE SUSUAL
i
GO RETURN
2163
2164
2165
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