External Bus Interface (EBI)MPC5566 Microcontroller Reference Manual, Rev. 2Freescale Semiconductor 12-23When no match is found on any of the chip select banks, the default transfer attributes shown inTable 12-12 are used.12.4.1.6 Burst Support (Wrapped Only)The EBI supports burst read accesses of external burstable memory. To enable bursts to a particularmemory region, clear the BI (Burst Inhibit) bit in the appropriate base register. External burst lengths of 4and 8 words are supported. Burst length is configured for each chip select by using the BL bit in theappropriate base register. See Section 12.4.2.5, “Burst Transfer” for more details.In 16-bit data bus mode (EBI_MCR[DBM] = 1), a special 2-beat burst case is supported for reads andwrites for 32-bit non-chip select accesses only. This is to allow 32-bit coherent accesses to another MCU.See Section 12.4.2.11, “Non-Chip-Select Burst in 16-bit Data Bus Mode.”Bursting of accesses that are not controlled by the chip selects is not supported for any other case besidesthe special case of 32-bit accesses in 16-bit data bus mode.Burst writes are not supported for any other case besides the special case of 32-bit non-chip select writesin 16-bit data bus mode. Internal requests to write more than 32 bits (such as a cache line) externally arebroken up into separate 32-bit or 16-bit external transactions according to the port size. SeeSection 12.4.2.6, “Small Accesses (Small Port Size and Short Burst Length)” for more detail on thesecases.12.4.1.7 Bus MonitorWhen enabled (via the BME bit in the EBI_BMCR), the bus monitor detects when no TA assertion isreceived within a maximum timeout period for non-chip select accesses (that is, accesses that use externalTA). The timeout for the bus monitor is specified by the BMT field in the EBI_BMCR. Each time a timeouterror occurs, the BMTF bit is set in the EBI_TESR. The timeout period is measured in external bus(CLKOUT) cycles. Thus the effective real-time period is multiplied (by two or four) when a configurablebus speed mode is used, even though the BMT field itself is unchanged.Table 12-12. Default Attributes for Transfers Other than Chip SelectCS Attribute Default Value CommentPS 0 32-bit port sizeBL 0 Burst is disabled – length is variableWEBS 0 Write enablesTBDIP 0 Burst is disabled – length variableBI 1 Burst inhibitedSCY 0 Transfer acknowledge (TA) used – length variableBSCY 0 Transfer acknowledge (TA) used – length variable
