ADE5166 datasheet(132/156 Pages) AD

132 / 156 page

ADE5166/ADE5169/ADE5566/ADE5569

Rev. B | Page 132 of 156

)

÷(1 + SBAUDF/64)

UART TIMER

Rx/Tx CLOCK

fCORE

UARTBAUDEN

Rx CLOCK

Tx CLOCK

TIMER 1/TIMER 2

Rx CLOCK

FRACTIONAL

DIVIDER

TIMER 1/TIMER 2

Tx CLOCK

÷32

÷2DIV + SBTH

Because Timer 2 has 16-bit autoreload capability, very low baud

rates are still possible. Timer 2 is selected as the baud rate generator

by setting RCLK and/or TCLK in the Timer/Counter 2 control

SFR (T2CON, Address 0xC8[5:4]). The baud rates for transmit

and receive can be simultaneously different. Setting RCLK and/or

TCLK puts Timer 2 into its baud rate generator mode, as shown in

Figure 107.

In this case, the baud rate is given by the following formula:

Mode 1 or Mode 3 Baud Rate =

Figure 106. UART Timer, UART Baud Rate

()

[]

(

RCAP

CORE

65536

−

Two SFRs, the enhanced serial baud rate control SFR (SBAUDT,

Address 0x9E) and UART timer fractional divider SFR (SBAUDF,

Address 0x9D), are used to control the UART timer. SBAUDT

is the baud rate control SFR; it sets up the integer divider (the DIV

bits, Bits[2:0]) and the extended divider (the SBTH bits, Bits[4:3])

for the UART timer.

UART Timer Generated Baud Rates

The high integer dividers in a UART block mean that high speed

baud rates are not always possible. In addition, generating baud

rates requires the exclusive use of a timer, rendering it unusable

for other applications when the UART is required. To address

this problem, each ADE5166/ADE5169/ADE5566/ADE5569

has a dedicated baud rate timer (UART timer) specifically for

generating highly accurate baud rates. The UART timer can be

used instead of Timer 1 or Timer 2 for generating very accurate

high speed UART baud rates, including 115,200 bps. This timer

also allows a much wider range of baud rates to be obtained. In

fact, every desired bit rate from 12 bps to 393,216 bps can be

generated to within an error of ±0.8%. The UART timer also

frees up the other three timers, allowing them to be used for

different applications. A block diagram of the UART timer is

shown in Figure 106.

The appropriate value to write to the DIV bits and the SBTH

bits can be calculated using the following formula, where fCORE is

defined in the POWCON SFR (see Table 26). Note that the DIV

value must be rounded down to the nearest integer.

()

log

⎟

⎠

⎞

⎜

⎝

⎛

Rate

Baud

SBTH

DIV

CORE

fCORE

T2 PIN

(P1.4/T2/FP23)

T2EX PIN

(P1.3/T2EX/FP24)

TR2

CONTROL

TL2

(8 BITS)

TH2

(8 BITS)

RELOAD

EXEN2

CONTROL

TRANSITION

DETECTOR

EXF 2

TIMER 2

INTERRUPT

RCAP2L

RCAP2H

TIMER 2

OVERFLOW

RCLK

TCLK

CLOCK

SMOD

TIMER 1

OVERFLOW

C/ T2 = 0

C/ T2 = 1

NOTE: AVAILABILITY OF ADDITIONAL

EXTERNAL INTERRUPT

P1.4/T2/FP23

Figure 107. Timer 2, UART Baud Rates

ADE5166 Datasheet(PDF) 132 Page - Analog Devices

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