FT201XS-R datasheet(32/49 Pages) FTDI

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FT201X USB I2C SLAVE IC Datasheet

Version 1.4

Document No.: FT_000627 Clearance No.: FTDI# 264

Figure 9.2: Data transfers with 7-bit and 10-bit addressing modes

Flow Control when Reading

When reading data, it is important to know if there is data available to read over I2C and if the data read

is valid. There are three methods by which to check whether the data being read is valid.

Checking the I2C_TXE# line, which indicates whether the transmit buffer is empty. This signal

can be mapped to the CBUS pins. This line does not indicate the number of bytes available. If the

line is asserted, there are one or more bytes in the transmit buffer. Note that the Transmit buffer

is the buffer which holds data which has come from the host computer and is going to be read by

the external I2C master.

Do a read over I2C (Master receiver, Slave transmitter) and check whether the FT-X

acknowledges the address phase. The FT-X will NAK the address phase if there is no data to read.

If bursting data, then there is not an address phase for each byte. In this case, it is not possible

to tell when the buffer has emptied and therefore when you are no longer reading valid bytes. In

this case, a Data Available check can be carried out first. If the byte after the general call address

is 0x0C (0000 1100), the FT-X returns the Data Available Count to indicate the number of bytes

available for burst read. Please also refer to section 9.3. Note that because this returns a single

byte, the maximum value is 0xFF, and so a value of 0xFF indicates that there are 255 or more

bytes available.

Figure 9.3: Checking the Data Available Count

Flow Control when Writing

When writing data (data going from I2C toward the host computer), it is important to check if there is

space available and if the FT-X accepted the byte written. There are two methods by which to check

whether space is available.

Check the I2C_RXF# line, which indicates whether the Receive buffer is full. This line indicates

that there is at least one empty byte available in the buffer. However, there is no indication of

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