Analog Devices ADSP-BF535 Blackfin, Hardware Reference Manual

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External Memory Design Issues
19-10 ADSP-BF535 Blackfin Processor Hardware Reference
Avoiding Bus Contention
Because the tristatable data bus is shared by multiple devices in a system,
be careful to avoid contention. Contention causes excessive power dissipa-
tion and can lead to device failure. Contention occurs during the time one
device is getting off the bus and another is getting on. If the first device is
slow to tristate and the second device is quick to drive, the devices
contend.
There are two cases where contention can occur. The first case is a read
followed by a write to the same memory space. In this case, the
ADSP-BF535 processor’s data bus drivers can potentially contend with
those of the memory device addressed by the read. The second case is
back-to-back reads from two different memory spaces. In this case, the
two memory devices addressed by the two reads can potentially contend at
the transition between the two read operations.
To avoid contention, program the turnaround time (Bank Transition
Time) appropriately in the Asynchronous Memory Bank Control Regis-
ters. This feature allows software to set the number of clock cycles
between these types of accesses on a bank by bank basis. Minimally, the
EBIU provides one cycle for the transition to occur.
Figure 19-4. Interface to 16-bit SRAM
ADSP-BF535
AMS[X]
AOE
AWE
ABE[1:0]
ADDR[N+1:2]
DATA[15:0]
ARE
ARDY
CE
OE
R/W
16-BIT SRAM
B[1:0]
A[N:1]
D[15:0]
ABE[3]/ADDR[1] A[0]