VRS51C1000
The value to write into the TH1 register is defined by
the following formula:
The following formula can be used to calculate the
baud rate in modes 1 and 3 using the Timer 2:
(NTD where are the formulas?)
Modes 1, 3 Baud Rate =
Oscillator Frequency
32x[65536 – (RCAP2H, RCAP2L)]
TH1 = 256 -
2SMODx Fosc
32 x 12x (Baud Rate)
Generating UART Baud Rates with Timer 2
The formula below is used to define the reload value to
put into the RCAP2h, RCAP2L registers to achieve a
given baud rate.
Timer 2 is often preferred to generate the baud rate, as
it can be easily configured to operate as a 16-bit timer
with auto-reload. This allows for much better resolution
than using Timer 1 in 8-bit auto-reload mode.
(RCAP2H, RCAP2L) = 65536 -
Fosc
32x[Baud Rate]
The baud rate using Timer 2 is defined as:
Mode 1,3 Baud Rate = Timer 2 Overflow Rate
16
In the above formula, RCAP2H and RCAP2L are the
content of RCAP2H and RCAP2L taken as a 16-bit
unsigned integer.
Note that a rollover in TH2 does not set TF2, and will
not generate an interrupt and because of this, Timer 2
interrupt does not have to be disabled when Timer 2 is
configured in baud rate generator mode.
The timer can be configured as either a timer or a
counter in any of its 3 running modes. In most typical
applications, it is configured as a timer (C/T2 is set to
0).
To make the Timer 2 operate as a baud rate generator,
the TCLK and RCLK bits of the T2CON register must
be set to 1.
Furthermore, when Timer 2 is configured as UART
baud rate generator and running (TR2 is set to 1), the
user should not try to perform read or write operations
to the TH2 or TL2 and RCAP2H, RCAP2L registers
The baud rate generator mode is similar to the auto-
reload mode in that an overflow in TH2 causes the
Timer 2 registers to be reloaded with the 16-bit value in
registers RCAP2H and RCAP2L, which are preset by
software. However, when Timer 2 is configured as a
baud rate generator, its clock source is Osc/2.
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