80C186EC/80C188EC Microprocessor User's Manual

SERIAL COMMUNICATIONS UNIT
mov dx, P1CON ;Get state of port 1 controls
in ax, dx
and ax, 0feh ;make sure P1.0 is port
out dx, al
mov dx, B1CMP
mov ax, tran_freq
or ax, 8000h ;set internal clocking bit
out dx, ax ;Mode 0, 1 million bps
mov dx, P2CON ;set Port 2.1 for TXD
mov ax, 0ffh
out dx, al
mov dx, S1TBUF ;send user's data
mov ax, user_data
out dx, al
mov dx, S1CON ;Mode 0, No CTS, Transmit
xor ax, ax
out dx, ax
mov dx, S1STS
Check_4_TI: in ax, dx
test ax, 0020h ;check for TI bit
jz Check_4_TI
_parallel_serial endp
lib_80186 ends
end
mov dx, P1LTCH ;pulse P1.0
xor ax, ax
out dx, al
not ax ;set P1.0 high
out dx, al
not ax ;set P1.0 low
out dx, al
pop dx ;restore saved registers
pop ax
pop bp ;restore user's bp
ret
Example 11-2. Mode 0 Example (Continued)
11.5.3 Master/Slave Example
This section shows an example of a Mode 2 and 3 master/slave network. Figure 11-18 shows the
proper connection of the master to the slaves. The buffer is necessary to avoid contention on the
receive line. Alternatively, an open-collector buffer could be used and the port pin function could
be deleted.
11-24