Zilog Z16C35 - Manual (Page 294)

Application Note
Technical Considerations When Implementing LocalTalk Link Access Protocol
14-6
LISTING 3
1131 ;******************************
1132 ;receive int service routine.
1133 ;******************************
1134 ;save received character in receiver buffer
1135 ;to by rxpointer
1136
0000044d 1137recint:
0000044d f5 1138 push af ;save af
0000044e d5 1139 push de
0000044f e5 1140 push hl
00000450 dbe9 1141 in a,(scc_data) ;read scc data
00000452 2aWwww 1142 ld hl,(rxpointer) ;
00000455 77 1143 ld (hl),a ;save it
00000456 23 1144 inc hl ;update pointer
00000457 22Www 1145 ld (rxpointer),hl ;
0000045a ed5bWwww 1146 ld de,(rxbufend) ;end of rx buffer
0000045e af 1147 xor a ;reset cy
0000045f ed52 1148 sbc hl,de ;
00000461 c2Wwww 1149 jp nz,recexit ;if not zero,then receive
byte length is ok
00000464 21Wwww 1150 ld hl,recerrflg ;
00000467 cbc6 1151 set 0,(hl) ;set bit0=1 maxfrmflg to indicate error
1152 ;because of max frame
size exceeded.
00000469 1153recexit:
00000469 3e38 1154 ld a,038h
0000046b d3e8 1155 out (scc_cont),a ;reset highest ius
0000046d e1 1156 pop hl
0000046e d1 1157 pop de
0000046f f1 1158 pop af ;restore af
00000470 fb 1159 ei ;enable int
00000471 c9 1160 ret ;return from int
1161 ;note ret and not reti is used for scc
1162 ;interrupts on the z80181.
1163
1164
;*********************************************
1165 ;special receive interrupt service routine
1166 ;*********************************************
1167; “parity is special condition” bit is off.
1168; special conditions are eof or rx overrun error.
1169; crc error flag is valid only if eof is valid.
1170; if frame is ok then recerrflg bit1=0, otherwise
1171
00000472 1172 spcond:
00000472 f5 1173 push af ;save af reg
00000473 c5 1174 push bc ;
00000474 e5 1175 push hl;
1176
00000475 3e01 1177 ld a,01h
00000477 d3e8 1178 out (scc_cont),a ;read rr1
00000479 dbe8 1179 in a,(scc_cont)
0000047b e660 1180 and 01100000b ;check bit6 (crc) or bit5 (overrun)
0000047d caWwww 1181 jp z,ok ;
1182 ;
00000480 21Wwww 1183 ld hl,recerrflg ;fetch receive error flag
00000483 cbce 1184 set 1,(hl) ;set bit1=1 for frame not ok
00000485 c3Wwww 1185 jp crc_exit
Page 288 of 316
UM011002-0808