Analog Devices ADuC812 manual Rclk or Tclk, CAP2 TR2 Mode, Off

ADuC812

Timer/Counter Operation Modes

The following paragraphs describe the operating modes for timer/ counter 2. The operating modes are selected by bits in the T2CON SFR as shown in Table XIX.

Table XIX. TIMECON SFR Bit Designations

RCLK (or) TCLK	CAP2	TR2	MODE
0	0	1	16-Bit Autoreload
0	1	1	16-Bit Capture
1	X	1	Baud Rate
X	X	0	OFF

16-Bit Autoreload Mode

In “Autoreload” mode, there are two options, which are selected by bit EXEN2 in T2CON. If EXEN2 = 0, then when Timer 2 rolls over it not only sets TF2 but also causes the Timer 2 registers to be reloaded with the 16-bit value in registers RCAP2L and RCAP2H, which are preset by software. If EXEN2 = 1, then Timer 2 still performs the above, but with the added feature that

a1-to-0 transition at external input T2EX will also trigger the 16-bit reload and set EXF2. The Autoreload mode is illustrated in Figure 30 below.

16-Bit Capture Mode

In the “Capture” mode, there are again two options, which are selected by bit EXEN2 in T2CON. If EXEN2 = 0, then Timer 2 is a 16-bit timer or counter which, upon overflowing, sets bit TF2, the Timer 2 overflow bit, which can be used to generate an inter- rupt. If EXEN2 = 1, then Timer 2 still performs the above, but a l-to-0 transition on external input T2EX causes the current value in the Timer 2 registers, TL2 and TH2, to be captured into regis- ters 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. The Capture Mode is illustrated in Figure 31.

The baud rate generator mode is selected by RCLK = 1 and/or TCLK = 1.

In either case if Timer 2 is being used to generate the baud rate, the TF2 interrupt flag will not occur. Hence Timer 2 interrupts will not occur so they do not have to be disabled. In this mode the EXF2 flag, however, can still cause interrupts and this can be used as a third external interrupt.

Baud rate generation will be described as part of the UART serial port operation in the following pages.

CORE	12
CLK
	C/T2 = 0
T2	C/T2 = 1
PIN

TRANSITION

DETECTOR

T2EX

PIN

TL2	TH2
(8-BITS) (8-BITS)
CONTROL
TR2
RELOAD
RCAP2L	RCAP2H

TF2

EXF2

TIMER INTERRUPT

CONTROL

EXEN2

Figure 30. Timer/Counter 2, 16-Bit Autoreload Mode

CORE	12
CLK
	C/T2 = 0
T2	C/T2 = 1
PIN

TRANSITION

DETECTOR

T2EX

PIN

TL2	TH2
(8-BITS) (8-BITS)
CONTROL
TR2
CAPTURE
RCAP2L	RCAP2H

TF2

EXF2

TIMER INTERRUPT

CONTROL

EXEN2

Figure 31. Timer/Counter 2, 16-Bit Capture Mode

–34– REV. B