80C32/80C52

MATRA MHS

Rev. E (31/08/95)

8

The capture mode is illustrated in Figure 7.

Figure 7. Timer 2 in Capture Mode.

In the auto-reload mode there are again two options,

which are selected by bit EXEN2 in T2CON.If

EXEN2 = 0, then when Timer 2 rolls over it does not only

set TF2 but also causes the Timer 2 register 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 does the above, but with the added feature that a

1-to-0 transition at external input T2EX will also trigger

the 16 bit reload and set EXF2.

The auto-reload mode is illustrated in Figure 8.

Figure 8. Timer in Auto-Reload Mode.

(MSB)

(LSB)

TF2

EXF2

RCLK

TCLK

EXEN2

TR2

C/T2

CP/RL2

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

Symbol

Position

Name and Significance

TF2

T2CON.7

Timer 2 overflow flag set by a Timer 2 overflow and must be cleared by software. TF2

will not be set when either RCLK = 1 OR TCLK = 1.

EXF2

T2CON.6

Timer 2 external flag set when either a capture or reload is caused by a negative

transition on T2EX and EXEN2 = 1. When Timer 2 interrupt is enabled, EXF2 = 1 will

cause the CPU to vector to the Timer 2 interrupt routine. EXF2 must be cleared by

software.

RCLK

T2CON.5

Receive clock flag. When set, causes the serial port to use Timer2 overflow pulses for its

receive clock in modes 1 and 3. RCLK = 0 causes Timer 1 overflow to be used for the

receive clock.

TCLK

T2CON.4

Transmit clock flag. When set, causes the serial port to use Timer 2 overflow pulses for

its transmit clock in modes 1 and 3. TCLK = 0 causes Timer 1 overflows to be used for

the transmit clock.

EXEN2

T2CON.3

Timer 2 external enable flag. When set, allows capture or reload to occur as a result of a

negative transition on T2EX if Timer 2 is not being used to clock the serial port.

EXEN2 = 0 causes Timer 2 to ignore events at T2EX.

TR2

T2CON.2

Start/stop control for Timer 2. A logic 1 starts the timer.

C/T2

T2CON.1

Timer or counter select. (Timer 2) 0 = Internal timer (OSC/12)

1 = External event counter (falling edge triggered).

CP/RL2

T2CON.0

Capture/Reload flag. When set, captures will occur on negative transitions at T2EX if

EXEN 2 = 1. When cleared, auto reloads will occur either with Timer 2 overflows or

negative transition at T2EX when EXEN2 = 1. When either RCLK = 1 or TCLK = 1, this

bit is ignored and the timer is forced to auto-reload on Timer 2 overflow.