80C186EC/80C188EC Microprocessor User's Manual

SERIAL COMMUNICATIONS UNIT
DisconnectMode:
mov dx, S1STS ; clear any pending exceptions
in ax,dx
mov dx, P1CON ; get state of port 1 controls
in ax, dx
and ax, 0f0h ; make sure P1.0:P1.3 is port
out dx, ax
mov dx, P2CON ; set P2.1 for TXD1, P2.0for RXD1
mov ax, 0ffh
out dx, ax
mov dx, P1LTCH ; make sure TXD latch is tristated
mov ax, TriStateDis
out dx, ax ; set P1.7 to zero
mov dx, S1CON ; select control register
mov ax, 0022h ; receive, Mode 2
out dx, ax
SelStatus: mov dx, S1STS ; select status register
Check_4_RI: in ax, dx ; get status
test ax, 0040h ; data waiting
jz Check_4_RI ; no: then keep checking
mov dx, S1SRUF ; yes: then get data
in ax, dx
cmp al, My_Address ; is slave_1 being addressed
jne SelStatus ; no: then ignore
mov dx, S1CON ; yes: then switch to Mode 3, transmit
mov ax, 0003h ; Mode 3
out dx, ax
mov dx, P1LTCH ; enable tristate buffer
mov ax, TriStateEna
out dx, ax ; gate TXD onto master’s RXD
mov dx, S1TBUF ; echo My_Address to the master
mov ax, My_Address
out dx, ax
mov dx, S1CON ; switch to receive mode
mov ax, 0023h ; Mode 3, receive
out dx, ax
Wait_4_Cmd: mov dx, S1STS ; select status register
in ax, dx ; get status
test ax, 0040h ; command waiting
jz Wait_4_Cmd ; no: then keep checking
mov dx, S1RBUF ; yes: then get command
in ax, dx
cmp
je
al, Disconnect ; Disconnect command
DisconnectMode ; yes: then disconnect RXD from network
Example 11-5. Master/Slave — The slave_1 Routine (Continued)
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