EM357-RTR datasheet(92/240 Pages) ETC2

92 / 240 page

EM351 / EM357

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

RECEIVE Segment

with NACK

RECEIVE Segment

with ACK

IDLE

START Segment

STOP Segment

TRANSMIT Segment

received ACK ?

YES

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 2 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

for 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.

8.5.4

Interrupts

TWI master controller interrupts are generated on the following events:

Bus command (SC_TWISTART/SC_TWISTOP) completed (0 to 1 transition of SC_TWICMDFIN)

Character transmitted and slave device responded with NACK

8-21

120-035X-000D

Preliminary

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