Motorola ColdFire MCF5281 - Manual (Page 227)

External Interface Module (EIM)
Freescale Semiconductor 13-3
Figure 13-2. Connections for External Memory Port Sizes
The timing relationship of chip selects (CS[7:0]), byte selects (BS[3:0]), and output enable (OE) with
respect to CLKOUT is similar in that all transitions occur during the low phase of CLKOUT. However,
due to differences in on-chip signal routing, signals may not assert simultaneously.
Figure 13-3. Chip-Select Module Output Timing Diagram
13.4.1 Bus Cycle Execution
When a bus cycle is initiated, the device first compares the address of that bus cycle with the base address
and mask configurations programmed for chip selects 0–7 (configured in CSCR0–CSCR7) and DRAM
block 0 and 1 address and control registers (configured in DACR0 and DACR1). If the driven address
compares with one of the programmed chip selects or DRAM blocks, the appropriate chip select is asserted
or the DRAM block is selected using the specifications programmed by the user in the respective
configuration register. Otherwise, the following occurs:
• If the address and attributes do not match in CSCR or DACR, the processor 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 processor runs an external burst-inhibited bus cycle with external termination
on a 32-bit port.
• Should an address and attribute match both DACRs or a DACR and a CSCR, the operation is
undefined.
Table 13-2 shows the type of access as a function of match in the CSCRs and DACRs.
Processor
Data Bus
Byte 0
8-Bit Port
16-Bit Port
32-Bit Port
Byte 1
Byte 2
Byte 3
Byte 0 Byte 1
Byte 2 Byte 3
Byte 0 Byte 1 Byte 2 Byte 3
D[31:24] D[23:16] D[15:8] D[7:0]
External
Memory
Memory
Memory
Byte Enable BS3 BS2 BS1 BS0
Driven with
indeterminate values
Driven with
indeterminate values
CS[7:0]
CLKOUT
BS[3:0]
OE
MCF5282 and MCF5216 ColdFire Microcontroller User’s Manual, Rev. 3