UPSD323X datasheet(56/176 Pages) STMICROELECTRONICS

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µPSD323X

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Figure 24. Timer/Counter Mode 3: Two 8-bit Counters

Mode 2. Mode 2 configures the Timer register as

an 8-bit Counter (TL1) with automatic reload, as

shown in Figure 23. Overflow from TL1 not only

sets TF1, but also reloads TL1 with the contents of

TH1, which is preset by software. The reload

leaves TH1 unchanged. Mode 2 operation is the

same for Timer/Counter 0.

Mode 3. Timer 1 in Mode 3 simply holds its count.

The effect is the same as setting TR1 = 0.

Timer 0 in Mode 3 establishes TL0 and TH0 as two

separate counters. The logic for Mode 3 on Timer

0 is shown in Figure 24. TL0 uses the Timer 0 con-

trol Bits: C/T, GATE, TR0, INT0, and TF0. TH0 is

locked into a timer function (counting machine cy-

cles) and takes over the use of TR1 and TF1 from

Timer 1. Thus, TH0 now controls the “Timer 1“ in-

terrupt.

Mode 3 is provided for applications requiring an

extra 8-bit timer on the counter. With Timer 0 in

Mode 3, an

µPSD323X Devices can look like it has

three Timer/Counters. When Timer 0 is in Mode 3,

Timer 1 can be turned on and off by switching it out

of and into its own Mode 3, or can still be used by

the serial port as a baud rate generator, or in fact,

in any application not requiring an interrupt.

Timer 2

Like timer 0 and 1, timer 2 can operate as either an

event timer or as an event counter. This is select-

ed by Bit C/T2 in the special function register

T2CON. It has three operating modes: capture,

autoload, and baud rate generator, which are se-

lected by bits in the T2CON as shown in Table 41.

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 which

upon overflowing sets Bit TF2, the Timer 2 over-

flow bit, which can be used to generate an inter-

rupt. 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 causes the cur-

rent 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. The Cap-

ture Mode is illustrated in Figure 25.

In the Auto-reload Mode, there are again two op-

tions, 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 regis-

ters to be reloaded with the 16-bit value in regis-

ters 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 Standard Serial Interface

(UART) Figure 26. The Baud Rate Generation

Mode is selected by (RCLK, RCLK1)=1 and/or

(TCLK, TCLK1)=1. It will be described in conjunc-

tion with the serial port.

AI06624

fOSC

TF0

Interrupt

Gate

TR0

INT0 pin

T0 pin

Control

TL0

(8 bits)

C/T = 0

C/T = 1

÷ 12

fOSC

TF1

Interrupt

Control

TH1

(8 bits)

÷ 12

TR1

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