EM357-RTR datasheet(90/241 Pages) SILABS

90 / 241 page

Rev 1.3

Full TWI frames have to be constructed by software from individual TWI segments. All necessary segment

transitions are shown in Figure 8.2. ACK or NACK generation of a TWI receive frame segment is determined with

the SC_TWIACK bit in the SCx_TWICTRL2 register.

Figure 8.2. TWI Segment Transitions

Generation of a 7-bit address is accomplished with one transmit segment. The upper 7 bits of the transmitted

character contain the 7-bit address. The remaining lower bit contains the command type (“read” or “write”).

Generation of a 10-bit address is accomplished with two transmit segments. The upper 5 bits of the first transmit

character must be set to 0x1E. The next 2 bits are for the two most significant bits of the 10-bit address. The

remaining lower bit contains the command type (“read” or “write”). The second transmit segment is for the

remaining 8 bits of the 10-bit address.

Transmitted and received characters are accessed through the SCx_DATA register.

To initiate (re)start and stop segments, set the SC_TWISTART or SC_TWISTOP bit in the SCx_TWICTRL1

waiting.

To initiate a transmit segment, write the data to the SCx_DATA data register, then set the SC_TWISEND bit in the

SCx_TWICTRL1 register, and finally wait until the bit is clear. Alternatively the SC_TWITXFIN bit in the

SCx_TWISTAT register can be used for waiting.

To initiate a receive segment, set the SC_TWIRECV bit in the SCx_TWICTRL1 register, wait until it is clear, and

then read from the SCx_DATA register. Alternatively, the SC_TWIRXFIN bit in the SCx_TWISTAT register can be

used for waiting. Now the SC_TWIRXNAK bit in the SCx_TWISTAT register indicates if a NACK or ACK was

received from a TWI slave device.

RECEIVE Segment

with NACK

RECEIVE Segment

with ACK

IDLE

START Segment

STOP Segment

TRANSMIT Segment

received ACK ?

YES

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