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Chapter 14. Timers/Counters and Serial Interface Page 14-7

Figure 14-3. Timer 0 - Mode 3

14.2.3 Timer Rate Control

By default, the FX2 timers increment every 12 CLKOUT cycles, just as in the standard 8051. Using

this default rate allows existing application code with real-time dependencies, such as baud rate, to

operate properly.

Applications that require fast timing can set the timers to increment every 4 CLKOUT cycles

instead, by setting bits in the Clock Control Register (CKCON) at SFR location 0x8E. (See

Table 14-4).

Each timer’s rate can be set independently. These settings have no effect in counter mode.

Table 14-4. CKCON (SFR 0x8E) Timer Rate Control Bits

Bit Function

CKCON.5 T2M - Timer 2 clock select. When T2M = 0, Timer 2 uses CLKOUT/12 (for

compatibility with standard 8051); when T2M = 1, Timer 2 uses CLKOUT/4.

This bit has no effect when Timer 2 is configured for baud rate generation.

CKCON.4 T1M - Timer 1 clock select. When T1M = 0, Timer 1 uses CLKOUT/12 (for

compatibility with standard 8051); when T1M = 1, Timer 1 uses CLKOUT/4.

CKCON.3 T0M - Timer 0 clock select. When T0M = 0, Timer 0 uses CLKOUT/12 (for

compatibility with standard 8051); when T0M = 1, Timer 0 uses CLKOUT/4.

TL0

Divide by 12

Divide by 4

T0 pin

TR0

GATE

INT0 pin 7

TF0

TH0

T0M

INT

TR1

TF1

INT

CLKOUT

CLK

C/ T

1 2 ... 294 295 296 297 298 299 300 301 302 303 304 ... 459 460

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