Intel 80312 I/O Companion Chip - ECEE

Intel ® 80312 I/O Companion ChipI 2 C Bus Interface Unit12.3.7 General Call AddressThe I 2 C unit supports both sending and receiving general call address transfers on the I 2 C bus.When sending a general call message from the I 2 C unit, software must set the General Call DisablebitintheICRtokeeptheI 2 C unit from responding as a slave. Failure to set this bit causes the I 2 CBus to enter an indeterminate state.A general call address is defined as a transaction with a slave address of 00H. When a devicerequires the data from a general call address, it acknowledges the transaction and stays inslave-receiver mode. Otherwise, the device can ignore the general call address. The second andfollowing bytes of a general call transaction are acknowledged by every device using it on the bus.Any device not using these bytes must not Ack. The meaning of a general call address is defined inthe second byte sent by the master-transmitter. Figure 12-15 shows a general call addresstransaction. The least significant bit (B) of the second byte defines the transaction. Table 12-7,“General Call Address Second Byte Definitions” on page 12-21 shows the valid values anddefinitions when B=0.When the companion chip is acting as a slave, and the I 2 C unit receives a general call address andtheICRGeneralCallDisablebitiscleartheI 2 C unit:• Sets the ISR general call address detected bit• Sets the ISR slave address detected bit• Interrupts (when enabled) the companion chipWhen the I 2 C unit receives a general call address and the ICR General Call Disable bit is set, theI 2 C unit ignores the general call address.Figure 12-15. General Call AddressSTART 00000000 ACKSecond Byte 0 ACKDataByteACKDataByteACKSTOPFirst ByteSecond ByteNBytes+ACKMaster to SlaveSlave to MasterLeast Significant Bit of Master AddressDefines Transaction12-20 Developer’s Manual