Specifications
67
3706C–MICRO–2/11
AT89LP3240/6440
Figure 12-7. Timer 2 Waveform: Dual Slope Modes
12.4 Baud Rate Generator
Timer 2 is selected as the baud rate generator b y setting TCLK and/or RCLK in T2CON (Table
12-3). Note that the baud rates for transmit and receive can be different if Timer 2 is used for the
receiver or transmitter and Timer 1 is us ed for the other function. S etting RCLK and/or TCLK
puts Timer 2 into its baud rate generator mode, as shown in Figure 12-8.
The baud rate generator mode is similar to the auto-reloa
d mode, in that a rollover in TH2
cau ses the Timer 2 registers to be reloaded with the 16-bit value in registers RCAP2H and
RCAP2L, which are preset by software.
The baud rates in UART Modes 1 and 3 are determined by Timer 2’s overflow rate according to
the following equation.
The Timer can be configured for either timer or counter operation. In most applications, it is con-
figured for timer operation (CP/T2
= 0). The baud rate formulas are given below.
where (RCAP2H, RCAP2L) is the content of RCAP2H and RCAP2L taken as a 16-bit unsigned
integer.
Timer 2 as a baud rate generator is shown in Figure 12-8. This figure is valid only if RCLK or
TCLK = 1 in T2CON. Note that a rollover in TH2 does not set TF2 and will not generate an inter-
rupt. Note too, that if EXEN2 is set, a 1-to-0 transition in T2EX will set EXF2 but will not cause a
reload from (RCAP2H, RCAP2L) to (TH2, TL2). Thus when Timer 2 i
s in use as a baud rate gen-
MAX
MIN
TOP
T2CM
1-0
= 10B
MAX
MIN
TOP
TF2 Set
TF2 Set
T2CM
1-0
= 11B
EXF2
Modes 1 and 3 Baud Rates
Timer 2 Overflow Rate
16
------------------------------------------------------------=
T2CM = 00B
Modes 1, 3
Baud Rate
Oscillator Frequency
16 TPS 1+()× 65536 RCAP2H,RCAP2L()–[]×
---------------------------------------------------------------------------------------------------------------------------------=
T2CM = 01B
Modes 1, 3
Baud Rate
Oscillator Frequency
16 TPS 1+()× RCAP2H RCAP2L(,)1+[]×
-------------------------------------------------------------------------------------------------------------------=