LTC6804 datasheet(42/90 Pages) AD

42 / 90 page

LTC6810-1/LTC6810-2

Rev. A

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OPERATION

COMM Commands

Three commands help accomplish I2C or SPI communica-

tion to the slave device: WRCOMM, STCOMM, RDCOMM

WRCOMM Command: This command is used to write

data to the COMM register. This command writes 6 bytes

of data to the COMM register. The PEC needs to be written

at the end of the data. If the PEC does not match, all data

in the COMM register is cleared to 1s when CSB goes

high. See the Bus Protocols section for more details on a

write command format.

STCOMM Command: This command initiates I2C/SPI

communication on the GPIO ports. The COMM register

contains 3 bytes of data to be transmitted to the slave.

During this command, the data bytes stored in the COMM

the data received from the I2C or SPI device is stored in

the COMM register. This command uses GPIO3 (SDA)

and GPIO4 (SCL) for I2C communication or GPIO2

(CSBM), GPIO3 (SDIOM) and GPIO4 (SCKM) for SPI

communication.

The STCOMM command is to be followed by 24 clock

cycles for each byte of data to be transmitted to the slave

device while holding CSB low. For example, to transmit 3

bytes of data to the slave, send STCOMM command and

its PEC followed by 72 clock cycles. Pull CSB high at the

end of the 72 clock cycles of STCOMM command.

During I2C or SPI communication, the data received from

the slave device is updated in the COMM register.

RDCOMM Command: The data received from the slave

device can be read back from the COMM register using the

RDCOMM command. The command reads back 6 bytes of

data followed by the PEC. See the Bus Protocols section

for more details on a read command format.

Table 24 describes the possible read back codes for

ICOMn[3:0] and FCOMn[3:0] when using the part as an

I2C master. Dn[3:0] contains the data byte transmitted by

the I2C slave.

In case of the SPI master, the read back codes for

ICOMn[3:0] and FCOMn[3:0] are always 0111 and 1111

respectively. Dn[3:0] contains the data byte transmitted

by the SPI slave.

Table 24. Read Codes for ICOMn[3:0] and FCOMn[3:0] on I2C Master

CONTROL BITS

CODE DESCRIPTION

ICOMn[3:0]

0110

Master generated a START signal.

0001

Master generated a STOP signal.

0000

Blank, SDA was held low between bytes.

0111

Blank, SDA was held high between bytes.

FCOMn[3:0]

0000

Master generated an ACK signal.

0111

Slave generated an ACK signal.

1111

Slave generated a NACK signal.

0001

Slave generated an ACK signal, master

generated a STOP signal.

1001

Slave generated a NACK signal, master

generated a STOP signal.

Figure 18 illustrates the operation of LTC6810 as an I2C

or SPI master using the GPIOs.

Figure 18.

68101 F18

COMM

GPIO

PORT

I2C/SPI

SLAVE

PORT A

RDCOMM

WRCOMM

STCOMM

LTC6810-1/LTC6810-2

LTC6810 I2C/SPI Master using GPIOs

Any number of bytes can be transmitted to the slave in

groups of 3 bytes using these commands. The GPIO

ports will not get reset between different STCOMM com-

mands. However, if the wait time between the commands

is greater than 2s, the watchdog will time out and reset

the ports to their default values.

To transmit several bytes of data using an I2C master,

a START signal is only required at the beginning of the

entire data stream. A STOP signal is only required at the

end of the data stream. All intermediate data groups can

use a BLANK code before the data byte and an ACK/NACK

signal as appropriate after the data byte. SDA and SCL

will not get reset between different STCOMM commands.

To transmit several bytes of data using SPI master, a

CSBM low signal is sent at the beginning of the 1st data

byte. CSBM can be held low or taken high for intermediate

data groups using the appropriate code on FCOMn[3:0].

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