Motorola ColdFire MCF5281 - Manual (Page 110)

Static RAM (SRAM)
5-2 Freescale Semiconductor
The RAMBAR contains several control fields. These fields are shown in Figure 5-1
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
Field BA31 BA30 BA29 BA28 BA27 BA26 BA25 BA24 BA23 BA22 BA21 BA20 BA19 BA18 BA17 BA16
Reset Undefined
R/W W
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Field — PRI1 PRI2 SPV WP — C/I SC SD UC UD V
Reset Undefined 0
R/W W
Address CPU + 0xC05
Figure 5-1. SRAM Base Address Register (RAMBAR)
Table 5-1. SRAM Base Address Register
Bits Name Description
31–16 BA Base address. Defines the 0-modulo-64K base address of the SRAM module. By
programming this field, the SRAM may be located on any 64-Kbyte boundary within the
processor’s 4-Gbyte address space.
15–12 — Reserved, should be cleared.
11–10 PRI1, PRI2 Priority bit. PRI1 determines if DMA or CPU has priority in upper 32k bank of memory. PRI2
determines if DMA or CPU has priority in lower 32k bank of memory. If bit is set, CPU has
priority. If bit is cleared, DMA has priority. Priority is determined according to the following
table.
NOTE: The Freescale-recommended setting for the priority bits is 00.
9 SPV Secondary port valid. Allows access by DMA
0 DMA access to memory is disabled.
1 DMA access to memory is enabled.
NOTE: The BDE bit in the second RAMBAR register must also be set to allow dual port
access to the SRAM. For more information, see
Section 8.4.2, “Memory Base Address
Register (RAMBAR) .”
8 WP Write protect. Allows only read accesses to the SRAM. When this bit is set, any attempted
write access will generate an access error exception to the ColdFire processor core.
0 Allows read and write accesses to the SRAM module
1 Allows only read accesses to the SRAM module
7–6 — Reserved, should be cleared.
PRI[1:2]
Upper Bank
Priority
Lower Bank
Priority
00 DMA Accesses DMA Accesses
01 DMA Accesses CPU Accesses
10 CPU Accesses DMA Accesses
11 CPU Accesses CPU Accesses
MCF5282 and MCF5216 ColdFire Microcontroller User’s Manual, Rev. 3