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问 我现在急需价位较低的51内核双串口单片机! 答 1: 用4016切换；或做个软的，3，4个都可以如题 wire@tom.com 答 2: 给你个2400的tx_byte:           clr  c
                   mov  r6,#8
                   clr  p1.6     ; low for start bit
resend:            call one      ; delay for one bit
                   rrc  a        ; shift to c
                   jnc  send_0   ; low, go sending 0
                   setb p1.6     ; high, send 1
decr6:             djnz r6, resend ; r6 = r6-1
                   call one
stop_bit:          setb p1.6     ; high for stop bit
                   call one                
                   ret
send_0:
                   clr  p1.6     ; low, send 0
                   sjmp decr6
;77777777777777777777777777777777777777777777777777777777777777777777777
rx_byte:                   
                   mov   r6,#8
fromfi:            jb    p1.7,$     ; high, if f0 being set
                   call  one_half   ; delay halt bit
gogo:              call  rxone        ; delay one bit                     
                   jb    p1.7,setone  ; high, go to set 1
                   clr   c          ; low  set 0
shift:             rrc   a          ; shift to c
                   djnz  r6,gogo    ; next bit
                   call  one   
                   ret
setone:            setb c           ; set 1
                   sjmp  shift
fi:                jnb   f0,fromfi  ; f0=0
                   ret                ; f0=1
one:         mov r5,#197 ; delay for 197x2 instruction time
             djnz r5,$
             ret
one_half:    
             mov r5,#90    ; delay for 96 instruction time
             djnz r5,$
             ret
rxone:             mov r5,#192;
                   djnz r5,$
                   ret


答 3: 用77E58算了 答 4: 速率不高的话可以用软件模拟一个 答 5: 价位较低多少？  25元以下可以吗