Intel Embedded Microcontroller Timer 1 Generated Baud Rates for Serial I/O Modes 1, SMOD1, Osc

8XC251SA, SB, SP, SQ USER’S MANUAL

Table 10-4. Timer 1 Generated Baud Rates for Serial I/O Modes 1 and 3

	Baud	Oscillator			Timer 1
		Frequency	SMOD1
	Rate					Reload
		(FOSC)		C/T#	Mode
						Value
62.5	Kbaud (Max)	12.0 MHz	1	0	2	FFH
19.2	Kbaud	11.059 MHz	1	0	2	FDH
9.6	Kbaud	11.059 MHz	0	0	2	FDH
4.8	Kbaud	11.059 MHz	0	0	2	FAH
2.4	Kbaud	11.059 MHz	0	0	2	F4H
1.2	Kbaud	11.059 MHz	0	0	2	E8H
137.5 Baud		11.986 MHz	0	0	2	1DH
110.0 Baud		6.0 MHz	0	0	2	72H
110.0 Baud		12.0 MHz	0	0	1	FEEBH

10.6.3.3Timer 2 Generated Baud Rates (Modes 1 and 3)

Timer 2 may be selected as the baud rate generator for the transmitter and/or receiver (Figure 10-5). The timer 2 baud rate generator mode is similar to the auto-reload mode. A rollover in the TH2 register reloads registers TH2 and TL2 with the 16-bit value in registers RCAP2H and RCAP2L, which are preset by software.

The timer 2 baud rate is expressed by the following formula:

Timer 2 Overflow Rate

Serial I/O Modes 1 and 3 Baud Rate = -----------------------------------------------------------

16

10.6.3.4Selecting Timer 2 as the Baud Rate Generator

To select timer 2 as the baud rate generator for the transmitter and/or receiver, program the RCLCK and TCLCK bits in the T2CON register as shown in Table 10-5. (You may select differ- ent baud rates for the transmitter and receiver.) Setting RCLK and/or TCLK puts timer 2 into its baud rate generator mode (Figure 10-5). In this mode, a rollover in the TH2 register does not set the TF2 bit in the T2CON register. Also, a high-to-low transition at the T2EX pin sets the EXF2 bit in the T2CON register but does not cause a reload from (RCAP2H, RCAP2L) to (TH2, TL2). You can use the T2EX pin as an additional external interrupt by setting the EXEN2 bit in T2CON.

NOTE

Turn the timer off (clear the TR2 bit in the T2CON register) before accessing registers TH2, TL2, RCAP2H, and RCAP2L.

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