Zilog Z16C35 Manual do Utilizador descarregar pdf (Página 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

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