DVR21 datasheet(223/416 Pages) MICROCHIP

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DS30010118D-page 223

PIC24FJ256GA705 FAMILY

18.2

Setting Baud Rate When

Operating as a Bus Master

To compute the Baud Rate Generator reload value, use

Equation 18-1.

EQUATION 18-1:

COMPUTING BAUD RATE

RELOAD VALUE(1,2,3)

18.3

Slave Address Masking

The I2CxMSK register (Register 18-4) designates

address bit positions as “don’t care” for both 7-Bit and

10-Bit Addressing modes. Setting a particular bit

location (= 1) in the I2CxMSK register causes the slave

module to respond, whether the corresponding address

bit value is a ‘0’ or a ‘1’. For example, when I2CxMSK is

set to ‘0010000000’, the slave module will detect both

addresses, ‘0000000000’ and ‘0010000000’.

To enable address masking, the Intelligent Peripheral

Management Interface (IPMI) must be disabled by

clearing the STRICT bit (I2CxCONL<11>).

TABLE 18-2:

I2Cx RESERVED ADDRESSES(1)

Note 1: Based on FCY = FOSC/2; Doze mode

and PLL are disabled.

2: These clock rate values are for

guidance only. The actual clock rate

can be affected by various system-

level parameters. The actual clock rate

should be measured in its intended

application.

3: BRG values of 0 and 1 are forbidden.

FSCL =

FCY

(I2CxBRG + 2) * 2

[ FCY

(FSCL * 2)

– 2

or:

]

I2CxBRG =

Note:

As a result of changes in the I2C protocol,

the addresses in Table 18-2 are reserved

and will not be Acknowledged in Slave

mode. This includes any address mask

settings that include any of these

addresses.

TABLE 18-1:

I2Cx CLOCK RATES(1,2)

Required System FSCL

FCY

I2CxBRG Value

Actual FSCL

(Decimal)

(Hexadecimal)

100 kHz

16 MHz

100 kHz

8 MHz

100 kHz

4 MHz

100 kHz

400 kHz

16 MHz

400 kHz

8 MHz

400 kHz

4 MHz

400 kHz

1MHz

16 MHz

1.000 MHz

1MHz

8MHz

1.000MHz

Note 1:

Based on FCY = FOSC/2; Doze mode and PLL are disabled.

These clock rate values are for guidance only. The actual clock rate can be affected by various

system-level parameters. The actual clock rate should be measured in its intended application.

Slave Address

R/W Bit

Description

0000 000

General Call Address(2)

0000 000

Start Byte

0000 001

Cbus Address

0000 01x

Reserved

0000 1xx

HS Mode Master Code

1111 0xx

10-Bit Slave Upper Byte(3)

1111 1xx

Reserved

Note 1:

The address bits listed here will never cause an address match independent of address mask settings.

This address will be Acknowledged only if GCEN = 1.

A match on this address can only occur on the upper byte in 10-Bit Addressing mode.

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