INTERNAL SPECIFICATIONS

4.6.3.4Mode 3

4.6.3.4.1 Outline

Mode 3 is another 11-bit frame UART mode (with one start bit, eight data bits, one multi- purpose data bit, and one stop bit). Whereas the baud rate is 1/64th or 1/32nd of the fundamental oscillator frequency in mode 2, the mode 3 baud rate can be freely selected according to the timer/counter 1 or timer/counter 2 setting. Apart from the ability to vary the baud rate, mode 3 is identical to mode 2.

A block diagram of the serial port in mode 3 is shown in Figure 4-35, and the operational timing chart is given in Figure 4-36.

4.6.3.4.2 Mode 3 baud rate

As in mode 1, the timer/counter 1 or timer/counter 2 overflow can be set as the baud rate clock source in mode 3 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

1

 

1

(SMOD=0)

2

 

16

 

 

 

 

B = fTC1

1

 

 

 

(SMOD=1)

16

 

 

 

 

 

 

Where B is the baud rate and fTC1 is the timer/counter 1 overflow frequency.

When timer/counter 1 is used as a timer in auto reload mode (mode 2), the baud rate is determined by the following equations.

B = fOSC

1

1

1

 

1

(SMOD=0)

12

256-DTH1

2

 

16

 

 

 

 

 

 

B = fOSC

1

1

1

 

 

 

(SMOD=1)

12

256-DTH1

16

 

 

 

 

 

 

 

 

where B is the baud rate, fOSC the fundamental oscillator (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, the baud rate is determined by the following equation.

B = fT2

1

1

65536-DRCAP2

16

 

 

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 by the following way.

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Sonic Alert msm83c154s, msm80154s, msm85c154hvs user manual Mode Outline, Mode 3 baud rate