Rainbow Electronics AT89LP216 - Manual (Page 40)

40
3621A–MICRO–6/06
AT89LP216 [Preliminary]
17.2 Baud Rates
The baud rate in Mode 0 is fixed as shown in the following equation:
The baud rate in Mode 2 depends on the value of the SMOD1 bit in Special Function Register
PCON.7. If SMOD1 = 0 (the value on reset), the baud rate is 1/32 of the oscillator frequency. If
SMOD1 = 1, the baud rate is 1/16 of the oscillator frequency, as shown in the following equation:
17.2.1 Using Timer 1 to Generate Baud Rates
The Timer 1 overflow rate determines the baud rates in Modes 1 and 3. When Timer 1 is the
baud rate generator, the baud rates are determined by the Timer 1 overflow rate and the value
of SMOD1 according to the following equation:
The Timer 1 interrupt should be disabled in this application. The Timer itself can be configured
for either timer or counter operation in any of its 3 running modes. In the most typical applica-
tions, it is configured for timer operation in auto-reload mode (high nibble of TMOD = 0010B). In
this case, the baud rate is given by the following formula:
Programmers can achieve very low baud rates with Timer 1 by configuring the Timer to run as a
16-bit auto-reload timer (high nibble of TMOD = 0001B). In this case, the baud rate is given by
the following formula.
Mode 0 Baud Rate
Oscillator Frequency
2
------------------------------------------------------- =
Mode 2 Baud Rate
2
SMOD1
32
-------------------- (Oscillator Frequency) ×
=
Modes 1, 3
Baud Rate
2
SMOD1
32
-------------------- (Timer 1 Overflow Rate)
×
=
Modes 1, 3
Baud Rate
2
SMOD1
32
--------------------
Oscillator Frequency
256 TH1
( )
–
[ ]
-------------------------------------------------------
1
TPS
1 +
-------------------- Ч Ч
=
Modes 1, 3
Baud Rate
2
SMOD1
32
--------------------
Oscillator Frequency
256
R
H1,RL1
( )
–
[ ]
------------------------------------------------------- ×
1
TPS
1 +
-------------------- Ч
=