Motorola MCF5281, MCF5282 user manual General Chip Select Operation

Chip Select Operation

12.3 Chip Select Operation

Each chip select has a dedicated set of registers for configuration and control.

•Chip select address registers (CSARn) control the base address of the chip select. See Section 12.4.1.1.

•Chip select mask registers (CSMRn) provide 16-bit address masking and access control. See Section 12.4.1.2.

•Chip select control registers (CSCRn) provide port size and burst capability indication, wait-state generation, and automatic acknowledge generation features. See Section 12.4.1.3.

CS0 is a global chip select after reset and provides relocatable boot ROM capability.

12.3.1 General Chip Select Operation

When a bus cycle is initiated, the MCF5282 first compares its address with the base address and mask configurations programmed for chip selects 0–6 (configured in CSCR0–CSCR6) and DRAM blocks 0 and 1 (configured in DACR0 and DACR1). If the driven address matches a programmed chip select or DRAM block, the appropriate chip select is asserted or the DRAM block is selected using the specifications programmed in the respective configuration register. Otherwise, the following occurs:

•If the address and attributes do not match in CSAR or DACR, the MCF5282 runs an external burst-inhibited bus cycle with a default of external termination on a 32-bit port.

•Should an address and attribute match in multiple CSCRs, the matching chip select signals are driven; however, the chip select signals are driven during an external burst-inhibited bus cycle with external termination on a 32-bit port.

•If the address and attribute match both DACRs or a DACR and a CSAR, the operation is undefined.

Table 12-3 shows the type of access as a function of match in the CSARs and DACRs.

MOTOROLA Chapter 12. Chip Select Module 12-3