Zilog Z16C35 User Manual
Page 290
Application Note
Technical Considerations When Implementing LocalTalk Link Access Protocol
14-10
LISTING 2
600 ;*************************************************
601
;Subroutine to transmit the llapenq packet
602 ;*************************************************
00000244
603 txenq:
604
00000244 f5
605
push
af
;save status and a reg
00000245 c5
606
push
bc
;save
00000246 e5
607
push
hl
;save
608 ;
00000247 f3
609
di
;make sure that
610
;no interrupt routine
611
;nor should interrupt
612
;occur during
613 ;this
subroutine.
00000248 3e03
614
ld
a,03h
0000024a d3e8
615
out
(scc_cont),a
;WR3
0000024c 3ecc
616
ld
a,0cch
0000024e d3e8
617
out
(scc_cont),a
;8b/char,rx crc
618 ;enable,addrs
src
619
;and rx disabled
620
00000250 3e0a
621
ld
a,0ah
;select WR10
00000252 d3e8
622
out
(scc_cont),a
00000254 3ee0
623
ld
a,11100000b
;idle with flags
00000256 d3e8
624
out
(scc_cont),a
625
626
;****enable transmitter *****
00000258 3e05
627
ld
a,05h
;select WR5
0000025a d3e8
628
out
(scc_cont),a
0000025c 3e68
629
ld
a,01101000b
;enable tx
0000025e d3e8
630
out
(scc_cont),a
631 ;
632 ;
633
;****enable rs-422 driver *****
00000260 3e05
634
ld
a,05h
;select WR5
00000262 d3e8
635
out
(scc_cont),a
00000264 3e6a
636
ld
a,01101010b
;enable tx,
00000266 d3e8
637
out
(scc_cont),a
;reset rts
00000268 00
638
nop
00000269 00
639
nop
640
;nop’s needed to complete 4.3 usec
641
;for 1 bit time enable of transmitter.
642
;total delay=2*(7+11+4) T states at 10 MHZ
643 ;
644
;****disable rs-422 driver for 2 bit times*****
0000026a 3e05
645
ld
a,05h
;select WR5
0000026c d3e8
646
out
(scc_cont),a
0000026e 3e68
647
ld
a,01101000b
;enable tx, set rts
00000270 d3e8
648
out
(scc_cont),a
649 ;
00000272 3e80
650
ld
a,10000000b
;reset txcrc
00000274 d3e8
651
out
(scc_cont),a
00000276 0601
652
ld
b,01h
;delay count
00000278
653 csloop:
00000278 10fe
654
djnz
csloop
;loop needed
655 ;to
complete
656
;8.6 usec min.
657
;or 2 bit times.
658
;****enable rs-422 driver for llap transmission*****
0000027a 3e05
659
ld
a,05h
;select WR5
Page 284 of 316
UM011002-0808