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MSM80C154S/83C154S/85C154HVS
110
4.6.3.2 Mode 1
4.6.3.2.1 Outline
Mode 1 is the 10-bit frame UART mode (with one start bit, eight data bits, and one stop bit)
where the baud rate may be set to any value depending on the timer/counter 1 or timer/
counter 2 setting.
A block diagram of the serial port in mode 1 is shown in Figure 4-31, and the operational timing
chart is given in Figure 4-32.
4.6.3.2.2 Mode 1 baud rate
The timer/counter 1 or timer/counter 2 overflow can be set as the baud rate clock source in
mode 1 by independent TCLK and RCLK setting for the transmit and receive circuits.
Where the baud rate is determined by the timer/counter 1 overflow, baud rate is determined
by the overflow frequency and SMOD value according to the following equations.
B = fTC1 ×
2
1
× (SMOD=0)
B = f
TC1 × (SMOD=1)
16
1
16
1
where B is the baud rate and fTC1 is the timer/counter 1 overflow frequency.
When timer/counter 1 is used as a timer (internal clock) in auto reload mode (mode 2), the
baud rate is determined by the following equations.
B = fOSC ×
256-DTH1
1
× (SMOD=0)
(SMOD=1)
12
1
2
1
×
16
1
×
B = f
OSC ×
256-DTH1
1
×
12
1
×
16
1
where B is the baud rate, fOSC the fundamental (XTAL1·2) frequency, and DTH1 the TH1
contents (expressed in decimal).
Where the timer/counter 2 overflow serves as the baud rate clock source, the baud rate is
determined by the overflow frequency irrespective of the SMOD value.
When timer/counter 2 is used as a counter (external clock), the baud rate is determined by
the following equation.
B = fT2 ×
65536-DRCAP2
1
×
16
1
where B is the baud rate, fT2 the frequency of the clock applied to the T2 pin, and DRCAP2 the
contents of RCAP2L and RCAP2H (expressed in decimal).
Or if timer/counter 2 is used as a timer, the baud rate is determined in the following way.