Siemens AC75 - Manual (Page 503)

AC75 AT Command Set
19.8 AT^SSPI
s
AC75_ATC_V01.002 Page 503 of 569 10/30/06
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when the I²C slave device notifies that it has recognized the I²C Slave Address.
Not Acknowledge:
During a Transmit Transfer, a NAK is given when the I²C Slave Device notifies a failure to receive either the I²C
Slave Address or a data byte. In this case, a Stop Condition is sent to the I²C device.
During a Receive Transfer, a NAK is transmitted only when the I²C does not receive any reponse for the I²C Slave
Address. The I²C device never acknowledges the validity of the received data (by sending an ACK the master
acknowledges each received byte to the slave).