UPSD3233 datasheet(53/170 Pages) STMICROELECTRONICS

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uPSD3234A, uPSD3234BV, uPSD3233B, uPSD3233BV

Mode 2. Mode 2 configures the Timer register as

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

shown in Figure 23., page 51. 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., page 52. TL0 uses the

Timer 0 control Bits: C/T, GATE, TR0, INT0, and

TF0. TH0 is locked into a timer function (counting

machine cycles) and takes over the use of TR1

and TF1 from Timer 1. Thus, TH0 now controls the

“Timer 1“ Interrupt.

Mode 3 is provided for applications requiring an

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

Mode 3, an uPSD323X 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 Timers 0 and 1, Timer 2 can operate as either

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

lected 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., page 54. 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 tim-

er or counter which upon overflowing sets Bit TF2,

the Timer 2 Overflow Bit, which can be used to

generate an interrupt. 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 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 in-

terrupt. The Capture Mode is illustrated in Figure

25., page 55.

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., page 55. The Baud Rate Gen-

eration Mode is selected by (RCLK, RCLK1)=1

and/or (TCLK, TCLK1)=1. It will be described in

conjunction with the serial port.

Table 40. Timer/Counter 2 Control Register (T2CON)

543210

TF2

EXF2

RCLK

TCLK

EXEN2

TR2

C/T2CP/RL2

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