Holtek HT-IDE, User Manual

Page: 217 / 258

jmp receive ;no. test again
mov a,9 ;yes. start receiving
mov count,a ;load bit counter
mov a,b1 ;load delay counter
mov delay,a ;(+1 for timing adjustment)
rxdelay: ;
sdz delay ;delay to fit baudrate
jmp rxdelay ;
mov a,b1 ;reload delay counter
mov delay,a ;(+1 for timing adjustment)
sdz count ;if receive over?
jmp rxbit ;no. receive next bit
mov a,rcreg ;yes. put received data to Acc
ret ;
rxbit: ;
set c ;c=1
snz rx ;if received ’1’?
clr c ;no. c=0
rrc rcreg ;shift left through carry flag
jmp rxdelay ;repeat from rxdelay
receive endp ;
end
Program description
The most important element here is the baudrate parameter because the
transmiting and receiving of data have to be coordinated with the baudrate
speed. For this reason a formula as well as a table is provided to define this
constant. Because in this example the baudrate is not defined by using the
timer/counter some small discrepencies may exist, however according to
our tests using an 8051 the values given in the table are error free. The
higher the baudrate parameter the lower the error rate so by adjusting the
value of baudrate and system frequency the baudrate parameter value can
be raised.
Chapter 15 Input/Output Applications
207