I 2 C ModulesMCF5253 Reference Manual, Rev. 1Freescale Semiconductor 18-11Address MBAR+ $28C (MBSR)MBAR2+ $44C (MBSR2)Access: Supervisor or User read/write7 6 5 4 3 2 1 0R ICF IAAS IBB IAL SRW IIF RXAKWReset 1 0 0 0 0 0 0 1Figure 18-7. MBSR RegisterTable 18-6. MBSR Register Field DescriptionsField Description7ICFWhile one byte of data is being transferred, the Data Transferring Bit bit is cleared. It is set by the falling edge of the 9thclock of a byte transfer.1 Transfer complete0 Transfer in progress6IAASWhen its own specific address (I 2 C Address Register) is matched with the calling address, the Addressed as a SlaveBit is set. The CPU is interrupted provided the IIEN is set. Next, the CPU must check the SRW bit and set its TX/RXmode accordingly. Writing to the I 2 C Control Register clears this bit.1 Addressed as a slave0 Not addressed5IBBThe Bus Busy Bit indicates the status of the bus. When a START signal is detected, the IBB is set. If a STOP signal isdetected, it is cleared.1 Bus is busy0 Bus is idle4IALHardware sets the Arbitration Lost bit (IAL) when the arbitration procedure is lost. Arbitration is lost in the followingcircumstances:• SDA sampled as low when the master drives a high during an address or data-transmit cycle.• SDA sampled as a low when the master drives a high during the acknowledge bit of a data-receive cycle.• A start cycle is attempted when the bus is busy.• A repeated start cycle is requested in slave mode.• A stop condition is detected when the master did not request it.This bit must be cleared by software by writing a zero to it.3 Reserved2SRWWhen IAAS is set, the Slave Read/Write bit indicates the value of the R/W command bit of the calling address sent fromthe master. This bit is valid only when:• A complete transfer has occurred and no other transfers have been initiated.• I 2C is a slave and has an address match.Checking this bit, the CPU can select slave transmit/receive mode according to the command of the master.1 Slave transmit, master reading from slave0 Slave receive, master writing to slave
