MX10E8050X 查看數據表（PDF） - Macronix International

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MX10E8050X

Microcontroller

Macronix International 

PRELIMINARY

MX10E8050I /

MX10E8050IA

TIMER 2 OPERATION

Timer 2

Timer 2 is a 16-bit Timer/Counter which can operate as either an event timer or an event counter, as selected by C/

T2* in the special function register T2CON (see Figure 2). Timer 2 has three operating modes: Capture, Auto-reload

(up or down counting), and Baud Rate Generator, which are selected by bits in the T2CON as shown in Table 9.

Capture Mode

In the capture mode there are two options which are selected by bit EXEN2 in T2CON. If EXEN2=0, then timer 2 is a

16-bit timer or counter (as selected by C/T2* in T2CON) which, upon overflowing sets bit TF2, the timer 2 overflow bit.

This bit can be used to generate an interrupt (by enabling the Timer 2 interrupt bit in the IE register). If EXEN2= 1,

Timer 2 operates as described above, but with the added feature that a 1- to -0 transition at external input T2EX

causes the current value in the Timer 2 registers, TL2 and TH2, to be captured into registers RCAP2L and RCAP2H,

respectively. In addition, the transition at T2EX causes bit EXF2 in T2CON to be set, and EXF2 like TF2 can generate

an interrupt (which vectors to the same location as Timer 2 overflow interrupt. The Timer 2 interrupt service routine can

interrogate TF2 and EXF2 to determine which event caused the interrupt). The capture mode is illustrated in Figure B

(There is no reload value for TL2 and TH2 in this mode. Even when a capture event occurs from T2EX, the counter

keeps on counting T2EX pin transitions or osc/6 pulses (osc/12 in 12 clock mode).).

Auto-Reload Mode ( Up or Down Counter )

In the 16-bit auto-reload mode, Timer 2 can be configured (as either a timer or counter [C/T2* in T2CON]) then

programmed to count up or down. The counting direction is determined by bit DCEN (Down Counter Enable) which is

located in the T2MOD register (see Figure 4). When reset is applied the DCEN=0 which means Timer 2 will default to

counting up. If DCEN bit is set, Timer 2 can count up or down depending on the value of the T2EX pin.

Figure 5 shows Timer 2 which will count up automatically since DCEN=0. In this mode there are two options selected

by bit EXEN2 in T2CON register. If EXEN2=0, then Timer 2 counts up to 0FFFFH and sets the TF2 (Overflow Flag) bit

upon overflow. This causes the Timer 2 registers to be reloaded with the 16-bit value in RCAP2L and RCAP2H. The

values in RCAP2L and RCAP2H are preset by software means.

If EXEN2=1, then a 16-bit reload can be triggered either by an overflow or by a 1-to-0 transition at input T2EX. This

transition also sets the EXF2 bit. The Timer 2 interrupt, if enabled, can be generated when either TF2 or EXF2 are 1.

In Figure 6 DCEN=1 which enables Timer 2 to count up or down. This mode allows pin T2EX to control the direction

of count. When a logic 1 is applied at pin T2EX Timer 2 will count up. Timer 2 will overflow at 0FFFFH and set the TF2

flag, which can then generate an interrupt, if the interrupt is enabled. This timer overflow also causes the 16-bit value

in RCAP2L and RCAP2H to be reloaded into the timer registers TL2 and TH2.

When a logic 0 is applied at pin T2EX this causes Timer 2 to count down. The timer will underflow when TL2 and TH2

become equal to the value stored in RCAP2L and RCAP2H. Timer 2 underflow sets the TF2 flag and causes 0FFFFH

to be reloaded into the timer registers TL2 and TH2.

The external flag EXF2 toggles when Timer 2 underflows or overflows. This EXF2 bit can be used as a 17th bit of

resolution if needed. The EXF2 flag does not generate an interrupt in this mode of operation.

P/N:PM0887 Specifications subject to change without notice, contact your sales representatives for the most update information. REV. 1.6, MAR. 28, 2005

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