UPSD3422 datasheet(94/293 Pages) STMICROELECTRONICS

94 / 293 page

Standard 8032 timer/counters

uPSD34xx

94/293

Table 44.

Timer/Counter 2 Operating Modes

Note:

↓ = falling edge

20.6.3

Baud rate generator mode

The RCLK and/or TCLK Bits in the SFR T2CON allow the transmit and receive baud rates

on serial port UART0 to be derived from either Timer 1 or Timer 2. Figure 30 on page 98

illustrates Baud Rate Generator Mode.

When TCLK = 0, Timer 1 is used as UART0’s transmit baud generator. When TCLK = 1,

Timer 2 will be the transmit baud generator. RCLK has the same effect for UART0’s receive

baud rate. With these two bits, UART0 can have different receive and transmit baud rates -

one generated by Timer 1, the other by Timer 2.

Note:

Bits RCLK1 and TCLK1 in the SFR named PCON (see Section Table 26.: PCON: Power

Control Register (SFR 87h, reset value 00h) on page 66) have identical functions as RCLK

and TCLK but they apply to UART1 instead. For simplicity in the following discussions about

baud rate generation, no suffix will be used when referring to SFR registers and bits related

to UART0 or UART1, since each UART interface has identical operation. Example, TCLK or

TCLK1 will be referred to as just TCLK.

The Baud Rate Generator Mode is similar to the Auto-reload Mode, in that a roll over in TH2

causes the Timer 2 registers, TH2 and TL2, to be reloaded with the 16-bit value in Registers

RCAP2H and RCAP2L, which are preset with firmware.

The baud rates in UART Modes 1 and 3 are determined by Timer 2’s overflow rate as

follows:

UART Mode 1,3 Baud Rate =Timer 2 Overflow Rate / 16

Mode

Bits in T2CON SFR

T2X

Remarks

Input Clock

RCLK

TCLK

CP/

RL2

TR2 EXEN2

Timer,

Internal

Counter,

External

(Pin T2,

P1.0)

16-bit

Auto-

reload

reload [RCAP2H, RCAP2L] to

[TH2, TL2] upon overflow (up

counting)

fOSC/12

MAX

fOSC/24

↓

reload [RCAP2H, RCAP2L] to

[TH2, TL2] at falling edge on pin

T2X

16-bit

Capture

16-bit Timer/Counter (up

counting)

fOSC/12

MAX

fOSC/24

↓

Capture [TH2, TL2] and store to

[RCAP2H, RCAP2L] at falling

edge on pin T2X

Baud

Rate

Generato

No overflow interrupt request

(TF2)

fOSC/2

–

↓

Extra Interrupt on pin T2X, sets

TF2

Off

Timer 2 stops

–

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